Abnormality diagnosing method for torque detecting device and electric power steering device

ABSTRACT

An abnormality diagnosing method is provided for a torque detecting device and an electric power steering device is provided using the torque detecting device. Immediately after the power supply is turned on and before steering auxiliary control is started, initial diagnosis is performed to determine that each monitoring block for monitoring an abnormality of a signal processing circuit constituting a torque detecting device operates normally. The initial diagnosis determines that a monitoring block is operating normally, by inputting a normal signal and an abnormal signal to the monitoring block alternately, and finding that the monitoring block carries out normal diagnosis when it receives the normal signal and that it carries out abnormal diagnosis when it receives the abnormal signal. Once all of the monitoring blocks are determined as normal, the steering auxiliary control based on a steering torque detected by the torque detecting device is started.

TECHNICAL FIELD

The present invention relates to an abnormality diagnosing method for a torque detecting device, which has a monitoring function for always monitoring a torque sensor signal and a processing system thereof, and an electric power steering device.

BACKGROUND ART

According to an electric power steering device, which assists a steering force using an electric motor, an assist force is generally determined based on a steering torque detected by a torque sensor, so as to drive and control the electric motor.

For example, Patent Document 1 discloses a technology for detecting a failure of the electric power steering device. According to this technology, a control means for conducting motor control is monitored using a failure detection means, and a failure detected by the failure detection means is stored in a failure memory means. This allows appropriate failure analysis, because all necessary failure information is stored without omission.

PRIOR ART Patent Document

Patent Document 1: JP 2010-30393 A

SUMMARY OF THE INVENTION Problem to be Solved

However, the technology disclosed in Patent Document 1 does not take diagnosis of the failure detection means itself into consideration. Therefore, even when a serious failure is detected by the failure detection means, whether the failure actually occurred and whether it may be incorrect detection due to a failure of the failure detection means cannot be determined. Moreover, even if a failure occurs on the sensor side, there is a possibility that such an incorrect detection that the sensor side is normal is made due to a failure of the failure detection means. As a result, reliable motor control cannot be carried out.

Therefore, the present invention has an object to provide an abnormality diagnosing method for a torque detecting device, so as to provide a highly reliable torque detecting device, and an electric power steering device using the torque detecting device.

Solution to the Problem

In order to attain the object, according to a first aspect of the present invention, there is provided an abnormality diagnosing method of a torque detecting device, wherein the torque detecting device comprises at least: a coil pair for detecting a relative displacement between a first rotary shaft and a second rotary shaft, which are connected to each other via a torsion bar that generates a twist when receiving a torque, by corresponding the relative displacement to a change in impedance; a signal processing unit having a torque detecting function for processing an output signal from the coil pair when a magnetization signal is supplied to the coil pair, and outputting a torque detecting signal; and a monitoring unit for regularly monitoring an abnormality of the torque detecting function; the abnormality diagnosing method comprising: inputting a diagnosis signal to the monitoring unit before the torque detecting function starts an operation; and confirming that the monitoring unit is operating normally.

According to a second aspect of the present invention may comprise inputting a normal signal and an abnormal signal as signals for diagnosis alternately to the monitoring unit, diagnosing the monitoring unit as normal, when the normal signal is input, and determining the monitoring unit is operating normally when the monitoring unit is diagnosed as abnormal, when the abnormal signal is input.

Furthermore, according to a third aspect of the present invention, the normal signal, the abnormal signal, and the normal signal for diagnosis may be input in this order to the monitoring unit.

Moreover, according to a fourth aspect of the present invention, the monitoring unit may be a magnetization signal monitoring unit for monitoring a waveform of the magnetization signal, and the monitoring unit receives a normal signal having an ideal waveform of the magnetization signal, and an abnormal signal different in frequency from the normal signal as signals for diagnosis, instead of the magnetization signal to be monitored, for determining whether or not the magnetization signal monitoring unit is operating normally.

In addition, according to a fifth aspect of the present invention, a signal having one half the frequency of the normal signal may be input as the abnormal signal, for determining whether or not the magnetization signal monitoring unit is operating normally.

Furthermore, according to a sixth aspect of the present invention, the monitoring unit may be a phase monitoring unit for monitoring whether or not the torque detecting signal shifts a phase from that of the magnetization signal, and the monitoring unit receives the magnetization signal and the signal having the phase shifted from the magnetization signal via a phase shift circuit, as diagnosis signals, instead of the torque detecting signal to be monitored, for determining whether or not the phase monitoring unit is operating normally.

Additionally, according to a seventh aspect of the present invention, the signal processing unit may be configured to A/D-convert the torque detecting signal and output the resulting signal, and the monitoring unit is an ADC monitoring unit for monitoring an output value a voltage value to be monitored after an A/D conversion, and the monitoring unit receives a plurality of normal voltage values including a central voltage value within a regularly used voltage region of the torque detecting signal and a plurality of abnormal voltage values different from the normal voltage value, as diagnosis signals, instead of the voltage value to be monitored, for determining whether or not the ADC monitoring unit is operating normally.

Moreover, according to an eighth aspect of the present invention, the signal processing unit may comprise a counter for frequency-dividing the clock signal and generating a pulse with an excitation frequency of the magnetization signal, the monitoring unit comprises a CR oscillator and a pulse width memory unit for calculating a width of an output pulse of the CR oscillator using the clock signal, and the monitoring unit is a clock monitoring unit for monitoring an abnormality of the clock signal by calculating the width of the output pulse of the CR oscillator using the clock signal and comparing the calculated value to the width of the output pulse stored in the pulse width memory unit, and the monitoring unit receives the pulse with the excitation frequency generated by the counter, as a diagnosis signal, instead of the clock signal to be monitored, for determining whether or not the clock monitoring unit is operating normally.

Additionally, according to a ninth aspect of the present invention, the signal processing unit may comprise an oscillation unit for generating, based on a clock pulse, the magnetization signal with a sinusoidal wave to be supplied to the coil pair, the monitoring unit comprises a low-pass filter for monitoring, the low-pass filter receiving the magnetization signal output from the oscillation unit, and the monitoring unit is a clock frequency change monitoring unit for detecting a change in amplitude of an output from the low-pass filter, as a change in frequency of the clock pulse, and receives a regular clock signal and an abnormal clock signal different in an excitation frequency from the regular clock signal, as diagnosis signals, for determining whether or not the clock frequency change monitoring unit is operating normally.

Furthermore, according to a tenth aspect of the present invention, the clock frequency change monitoring unit may have a configuration for detecting whether or not at least either a peak value along an upper half wave of the output from the low-pass filter for monitoring or a lower-half wave of the output falls within a normal amplitude range, and receives two kinds of signals including an abnormal high frequency clock signal having a frequency higher than an allowable upper-limit frequency of the regular clock signal, and an abnormal low frequency clock signal having a frequency lower than an allowable lower-limit frequency for the regular clock signal, as the abnormal clock signals, for determining whether or not the clock frequency change monitoring unit is operating normally.

Moreover, according to an eleventh aspect of the present invention, the signal processing unit may further comprise: an AD converter for converting an analog signal corresponding to the torque to a digital signal; a memory unit for storing beforehand a gain correcting value and an offset correcting value for correcting a gain and an offset for the digital signal converted by the AD converter; a first correction and calculation unit for correcting the digital signal converted by the AD converter based on the gain correcting value and the offset correcting value stored in the memory unit and outputting the corrected value as the torque detecting signal; and a second correction and calculation unit for performing the same correcting operation as that of the first correction and calculation unit; and the monitoring unit is an operating logic monitoring unit for inputting the same signal to the first correction and calculation unit and the second correction and calculation unit to compare calculated results of the first correction and calculation unit and the second correction and calculation unit, and monitor whether or not the operating logic of the first correction and calculation unit is functioning normally, and in determining whether or not the operating logic monitoring unit is functioning normally, whether or not the operating logic monitoring unit is operating normally is determined by inputting to the second correction and calculation unit a different signal than that of the first correction and calculation unit, as a diagnosis signal, to confirm that the calculated results of the first correction and calculation unit and the second correction and calculation unit differ.

In addition, according to a twelfth aspect of the present invention, an inverted signal of the input signal to the first correction and calculation unit may be used as a different signal to be input to the second correction and calculation unit from that to be input to the first correction and calculation unit, for determining whether or not the operating logic monitoring unit is operating normally.

Furthermore, according to a thirteenth aspect of the present invention, the signal processing unit may be provided to correspond to the coil pair, is configured to output a main torque signal and a sub torque signal based on the output signals from the coil pair, and detects the abnormality of the torque detecting device based on diagnostic information including an abnormality diagnosis result from the monitoring unit, the main torque signal, and the sub torque signal.

Yet furthermore, according to a fourteenth aspect of the present invention, the sub torque signal when an abnormality is detected by the monitoring unit may be a predetermined fixed value.

Moreover, according to a fifteenth aspect of the present invention, the signal processing unit may be provided to correspond to two coil pairs, is configured, to output a main torque signal based on each of the output signals from the coil pairs, and detects an abnormality of the torque detecting device based on diagnostic information including the abnormality diagnosis result from the monitoring unit, and each main torque signal.

Yet furthermore, according to a sixteenth aspect of the present invention, the signal processing unit may be configured to calculate the main torque signal and the sub torque signal based on output signals from the coil pairs and output only the main torque signal, and the abnormality diagnosis result from the monitoring unit is a result from the monitoring unit for monitoring the abnormality of the signal processing unit by comparing the main torque signal to the sub torque signal.

Additionally, according to a seventeenth aspect of the present invention, the diagnostic information may include at least three kinds of information including: information that the abnormality diagnosis result from the monitoring unit is normal, information that the abnormality diagnosis result from the monitoring unit is abnormal, and information that an initial diagnostic unit is performing an initial diagnosis.

Yet furthermore, according to an eighteenth aspect of the present invention, the diagnostic information may be a pulse signal of a fixed period, when the abnormality diagnosis result from the monitoring unit is normal, a high level signal, when the abnormality diagnosis result from the monitoring unit is abnormal, and a low level signal, when the initial diagnostic unit is conducting the initial diagnosis.

Yet furthermore, according to a first aspect of a power steering device according to the present invention, there is provided an electric power steering device, comprising: a torque detecting device for detecting a steering torque to be input to a steering mechanism; a motor control unit for drive-controlling an electric motor to supply to a steering system a steering auxiliary power that reduces a driver's steering burden, based on at least a steering torque detected by the torque detecting device; and an initial diagnostic unit for diagnosing the torque detecting device using the abnormality diagnosing method of any one of the above first to thirteenth aspects of the present invention before the motor control unit starts drive-controlling the electric motor.

Advantageous Effect of the Invention

According to the abnormality diagnosing method for a torque detecting device according to the present invention, initial diagnosis for confirming whether a monitoring circuit itself is operating normally can be conducted. Therefore, it is possible to provide a reliable torque detecting device using this abnormality diagnosing method.

Moreover, according to the electric power steering device of the present invention, initial diagnosis of the torque detecting device is conducted using the aforementioned abnormality diagnosing method, thereby confirming that the torque detecting device is surely operating normally and then starting steering auxiliary control. Therefore, stability and reliability of steering auxiliary control can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall schematic diagram illustrative of an electric power steering device according to an embodiment;

FIG. 2 is a block diagram of a configuration of a torque detecting device;

FIG. 3 shows a peripheral configuration of a coil constituting a torque sensor;

FIG. 4 is a block diagram for explaining a concept of an initial diagnostic method;

FIG. 5 is a flow chart of initial diagnostic process steps executed by an initial diagnostic unit;

FIG. 6 is a block diagram illustrating a configuration of a magnetization signal monitoring unit;

FIG. 7A and FIG. 7B are graphs illustrating an example of a signal waveform for initial diagnosis of the magnetization signal monitoring unit;

FIG. 8 is a block diagram illustrating a configuration of a phase monitoring unit;

FIG. 9A and FIG. 9B are graphs illustrating an example of a signal waveform for initial diagnosis of the phase monitoring unit;

FIG. 10 is a block diagram of a configuration of a torque signal monitoring unit;

FIG. 11 is a block diagram of a configuration of a torque detecting device according to a second embodiment;

FIG. 12 shows a peripheral configuration of a coil constituting a torque sensor;

FIG. 13 is a block diagram of a detailed configuration of an abnormality detector;

FIG. 14 is a graph illustrating characteristic curves representing a relationship between a cutoff frequency of a low-pass filter and difference in voltage from peak value at 9 kHz;

FIG. 15A to FIG. 15D are graphs for explaining an output from a low-pass filter;

FIG. 16 is a block diagram of a monitoring unit diagnosing unit according to a third embodiment;

FIG. 17 is a flow chart of initial diagnostic process steps executed by the monitoring unit diagnosing unit;

FIG. 18 is a block diagram of a configuration of a torque detecting device;

FIG. 19 is a block diagram of a configuration of a torque detecting device according to a fourth embodiment;

FIG. 20 is a block diagram of a configuration of a clock monitoring unit;

FIG. 21 is a block diagram of a configuration of a torque detecting device according to a fifth embodiment;

FIG. 22A and FIG. 22B are graphs illustrating a set gain value and a setting offsetting value;

FIG. 23 is a block diagram of a configuration of a torque calculation unit;

FIG. 24 is a block diagram of a configuration of a torque detecting device according to a sixth embodiment;

FIG. 25A to FIG. 25C are graphs illustrating a diagnosis signal S;

FIG. 26A to FIG. 26C are graphs illustrating torque signals Tm and Ts according to the sixth embodiment;

FIG. 27 is a block diagram of a configuration of a torque detecting device according to a seventh embodiment;

FIG. 28A to FIG. 28C are graphs illustrating torque signals Tm and Ts according to the seventh embodiment;

FIG. 29 is a block diagram of a configuration of a torque detecting device according to an eighth embodiment;

FIG. 30A to FIG. 30C are graphs illustrating diagnosis signals S1 and S2 according to the eighth embodiment; and

FIG. 31A to FIG. 31C are graphs illustrating torque signals Tm1 and Tm2 according to the eighth embodiment.

DESCRIPTION OF EMBODIMENTS

An embodiment of the present invention will be described below with reference to the drawings.

(First Embodiment)

(Configuration)

FIG. 1 is an overall schematic diagram illustrative of an electric power steering device according to the present embodiment.

Reference numeral 1 in FIG. 1 denotes a steering wheel. A steering force given to this steering wheel 1 by a driver is transmitted to a steering shaft 2, which has an input shaft 2 a and an output shaft 2 b. One end of the input shaft 2 a of the steering shaft 2 is connected to the steering wheel 1, and the other end is connected to one end of the output shaft 2 b via a torque sensor 3 of a torque detecting device 30, to be described later.

The steering force transmitted to the output shaft 2 b is then transmitted to an intermediate shaft 5 via a universal joint 4, and then transmitted to a pinion shaft 7 via a universal joint 6. The steering force transmitted to this pinion shaft 7 is then transmitted to a tie rod 9 via a steering gear 8, thereby turning steering wheels, not illustrated. The steering gear 8 is configured in a rack and pinion form by a pinion 8 a connected to the pinion shaft 7 and a rack 8 b meshing with the pinion 8 a. The rack 8 b transforms the rotational movement transmitted to the pinion 8 a to a translatory movement.

A steering auxiliary mechanism 10, which transmits a steering auxiliary force to the output shaft 2 b, is connected to the output shaft 2 b of the steering shaft 2. The steering auxiliary mechanism 10 is provided with a reduction gear 11 connected to the output shaft 2 b, and an electric motor 12 connected to the reduction gear 11 to generate the steering auxiliary force for a steering system.

The torque sensor 3 is attached to the steering wheel 1, for detecting the steering torque transmitted to the input shaft 2 a, by corresponding a relative displacement (rotary displacement) between the input shaft 2 a and the output shaft 2 b, which are connected by a torsion bar, not illustrated, to an impedance change of a coil pair. A torque detection value T output from the torque sensor 3 is input to a controller 15.

The controller 15 operates based on the power supplied from an in-vehicle battery 17 (e.g., its rated voltage is 12V.) The negative electrode of the battery 17 is grounded, whereas the positive electrode is connected to the controller 15 via an ignition switch 18, which starts an engine, and is also connected to the controller 15 directly without the intervention of the ignition switch 18.

A speed detected value V detected by a speed sensor 16 in addition to the torque detection value T is input to the controller 15, thereby carrying out steering auxiliary control for applying the steering auxiliary power according to the input to the steering system. Specifically, a steering auxiliary torque instruction value used for an electric motor 12 to generate the above-mentioned steering auxiliary power is calculated in a known process, so as to carry out the feedback control of a drive current supplied to the electric motor 12 based on the calculated steering auxiliary torque instruction value and the motor current detected value.

Next, a configuration of the torque detecting device 30 will be explained in detail.

FIG. 2 is a block diagram of a configuration of the torque detecting device 30. The torque detecting device 30 is provided with the torque sensor 3 mentioned above. FIG. 2 illustrates a signal processing circuit (signal processing unit) 140, which carries out signal processing of the output signal from the coil pair when a magnetization signal is supplied to the coil pair constituting the torque sensor 3 and then outputs a torque detecting signal, and a diagnostic device 160 provided with monitoring units, each monitoring abnormality of each block in the signal processing circuit 140.

The torque sensor 3, as illustrated in FIG. 3 illustrative of a peripheral configuration of the coil, includes: a coil pair that is a combination of a first coil 22Aa and a second cold 22Ab; a yoke 81 around which the coils 22Aa and 22Ab are wound; a cylinder member 83; multiple windows 831 arranged on the outer peripheral region of the cylinder member 83 to face the coil pair; a torsion bar 84; and a sensor shaft 85. Note that the torsion bar 84, the sensor shaft 85, and the input shaft 2 a, and the output shaft 2 b of the steering shaft 2 are arranged coaxially.

The signal processing circuit 140 is mainly configured with a clock unit, a magnetization unit, a sensor unit, a signal processing unit, and a communication output unit.

The clock unit is provided with a CLK 141, which is constituted by a commercially available clock (e.g., a quartz oscillator). Moreover, the clock unit includes a counter 143 for frequency-dividing and converting a clock signal to a designated frequency (magnetization frequency) based on the clock signal output from the CLK 141 and the designated frequency (either A Hz or B Hz) selected by an SEL 142. A magnetization pulse output from the counter 143 is input to a magnetization waveform generating unit 144, which constitutes a magnetization unit.

The magnetization waveform generating unit 144 generates a magnetization signal with a selected frequency of either A Hz or B Hz based on the magnetization pulse input from the counter 143, and then outputs it to a sensor unit. In this situation, the generated magnetization signal is supplied to a main bridge circuit (bridge MAIN) 145 and a sub bridge circuit (bridge SUB) 149, which constitute a sensor unit.

The main bridge circuit 145 is provided with a coil pair including a first coil and a second coil. When a magnetization signal is supplied to the coil pair, a main differential amplifier 146 amplifies and outputs a difference (terminal voltage difference) between the terminal voltages of the first coil and the second coil. Such an output signal is input to a main rectification smoothing circuit 147 for rectifying and smoothing the signal, and is then output therefrom. A low-pass filter (LPF) 148 removes noise from the smoothed output signal, and outputs the resulting signal to a torque calculating circuit 153, which constitutes a signal processing unit. Note that explanations of operations of the sub bridge circuit 149, a sub differential amplifier 150, a sub rectifying and smoothing circuit 151, and an LPF 152 will be omitted here, because their operations are the same as those of the main bridge circuit 145 to the LPF 148.

The torque calculating circuit 153 is provided with a multiplexer (MUX) and an AD converter (ADC), and calculates a torque detecting signal based on signals (MAIN torque value and SUB torque value) output from the LPFs 148 and 152 to output it to a communication output circuit 154, which constitutes the communication output unit. The communication output circuit 154 outputs the torque detecting signal calculated by the torque calculating circuit 153 to the controller (ECU) 15.

The monitoring units of the diagnostic device 160 include: a magnetization pulse monitoring unit 161 for monitoring a magnetization pulse; a magnetization signal monitoring unit 162 for monitoring waveforms (frequency, DUTY, shape, offset, reduction, excessive oscillation, etc.) of the magnetization signal; a phase monitoring unit 163 for monitoring a phase of the magnetization signal; a differential amplitude monitoring unit 164 for monitoring an amplitude of the signal output from the differential amplifier 150; a MUX/ADC monitoring unit 165 for monitoring abnormality of the MUX and the ADC of the torque calculating circuit 153; a torque signal monitoring unit 166 for monitoring a torque detecting signal output from the torque calculating circuit 153, and a communication monitoring unit 167 for monitoring abnormality of the communication output unit 154. Various monitoring processes are carried out routinely during the steering auxiliary control, and when a certain abnormality is detected, it is then transmitted to the ECU 15 shortly thereafter.

Furthermore, the diagnostic device 160 is provided with an initial diagnostic unit 168 for diagnosing each monitoring unit. Immediately after power supply is switched on (or immediately after the ignition switch 18 is turned on) and before the ECU 15 side starts steering auxiliary control, the initial diagnostic unit 168 starts operation, and conducts initial diagnosis for diagnosing whether each monitoring unit is operating normally. This initial diagnosis subjects each monitoring unit to diagnosis successively. Moreover, setting a flag during initial diagnosis prevents the ECU 15 from using a torque sensor signal (i.e., prevents the steering auxiliary control.)

Once the initial diagnostic unit 168 starts an initial diagnosis, a normal and an abnormal signal as initial diagnosis signals are alternately input to each of the monitoring units to be diagnosed, and confirms that each of the monitoring units is operating normally. In this situation, the normal signal denotes a “normal” (i.e., diagnosis indicates it is normal) signal with the diagnostic result from a monitoring block that is functioning normally, when that signal is to be monitored, whereas the abnormal signal denotes an “abnormal” (i.e., diagnosis indicates it is abnormal) signal with the diagnostic result from the monitoring block that is functioning normally, when that signal is to be monitored.

As illustrated in FIG. 4, in a regular monitoring mode (regular diagnostic mode), a switch SW1 is turned on, and a regularly monitored signal (regular signal) is input to a monitoring block to diagnose the regular signal.

On the other hand, each of switches SW1 to SW3 is turned on or off in response to a switching signal at the initial diagnosis to input an initial diagnosis signal to the monitoring block. In the present embodiment, a normal signal, an abnormal signal, and a normal signal are input in this order as signals for the initial diagnosis. When inputting a normal signal, the switch SW2 is turned on, whereas when inputting an abnormal signal, the switch SW3 is turned on.

The output from the monitoring block is set to “0” when diagnosed as normal, whereas it is set to “1” when diagnosed as abnormal. The output from the monitoring block is input to an AND circuit. The AND circuit performs a logical AND operation of the output from the monitoring block and a flag mask Mask, and then outputs the resulting value as a final output signal from the monitoring unit. The flag mask Mask is used for selecting the monitoring unit to be diagnosed, and in the regular diagnostic mode, the Masks for all the monitoring blocks are set to “OFF (i.e., 1)”. On the other hand, in the initial diagnostic mode, only Masks for the monitoring blocks to be diagnosed are set to “OFF (i.e., 1)”, and Masks for the other monitoring blocks not to be diagnosed are set to “ON (i.e., 0)”.

FIG. 5 is a flowchart of initial diagnostic process steps executed by the initial diagnostic unit 168. As described above, the initial diagnostic process is carried out immediately after the power is turned on and before the ECU 15 starts the steering auxiliary control.

First of all, in Step S1, the initial diagnostic unit 168 turns “off (i.e., 1)” only the flag masks for monitoring blocks to be subjected to the initial diagnosis, whereas it turns “ON (i.e., 0)” the flag masks for the other monitoring blocks. Turning “off (i.e., 1)” only the flag masks for the target monitoring blocks in this manner makes outputs from the other monitoring units (see output from the AND gate in FIG. 4) “0” irrespective of the outputs from the other monitoring blocks (i.e., the monitoring functions of the monitoring blocks are made invalid). Note that monitoring blocks that need a flag mask are those of the magnetization pulse monitoring unit 161, the magnetization signal monitoring unit 162, the phase monitoring unit 163, the differential amplitude monitoring unit 164, and the torque signal monitoring unit 166.

In Step S2, the initial diagnostic unit 168 inputs a normal signal for the initial diagnosis of the monitoring block to be subjected to the initial diagnosis (i.e., the switch SW2 in FIG. 4 is turned on) to switch to the initial diagnostic normal mode, and processing then proceeds to Step S3.

In Step S3, the initial diagnostic unit 168 stands by until the initial diagnostic normal mode becomes stable, reads the outputs from all of the monitoring units, and determines whether or not all of the outputs are “0” and that no abnormality has occurred. At this time, when the occurrence of an abnormality is confirmed, it is determined that the monitoring function of that monitoring unit has an abnormality, and processing then proceeds to Step S4. In Step S4, a predetermined abnormality process (e.g., notification of the abnormality by the communication output circuit 154 etc.) is carried out, and the initial diagnostic process ends.

On the other hand, when it is determined in step S3 that no abnormality has occurred, processing proceeds to Step S5. In Step S5, the initial diagnostic unit 168 inputs the abnormal signal for the initial diagnosis to the monitoring blocks to be subjected to the initial diagnosis (the switch SW3 in FIG. 4 is turned on) to switch to an initial diagnostic abnormal mode.

Next, in Step S6, the initial diagnostic unit 168 stands by until the initial diagnostic abnormal mode becomes stable, confirms all of the outputs from the monitoring units, and determines whether or not only the output from the target monitoring unit is “1” and an abnormality has occurred. At this time, when it is not determined that an abnormality has occurred, it is determined that the monitoring function of the monitoring unit has an abnormality, and processing proceeds to Step S4.

On the other hand, when it is determined in Step S6 that an abnormality has occurred, processing proceeds to Step S7. In Step S7, the initial diagnostic unit 168 inputs a normal signal for the initial diagnosis to the monitoring block to be subjected to the initial diagnosis (the switch SW2 in FIG. 4 is turned on) to switch to the initial diagnostic normal mode.

Then, in Step S8, the initial diagnostic unit 168 stands by until the initial diagnostic normal mode becomes stable, confirms all of the outputs from the monitoring units, and determines whether or not no abnormality has occurred. When it is determined that an abnormality has occurred, it is determined that there is an abnormality at the monitoring function of the monitoring unit, and processing then proceeds to Step S4. On the other hand, when it is determined in Step S8 that no abnormality has occurred, processing proceeds to Step S9.

In Step S9, the initial diagnostic unit 168 determines whether or not the initial diagnosis of all the monitoring units has ended. When there is a monitoring unit that has not yet been subjected to the initial diagnosis, processing proceeds to Step S1 to switch to another target to be subjected to the initial diagnosis. When the initial diagnosis of all the monitoring units ends, the initial diagnostic process then ends.

Since there is such an initial diagnostic function for diagnosing the monitoring units themselves, the reliability of the monitoring functions of the monitoring units can be improved. That is, it is possible to prevent a case where the monitoring units is not capable of detecting an abnormality of the signal processing circuit 140 even though the abnormality actually occurs, and a case of erroneously detecting an abnormality occurring in a monitoring unit, although the signal processing circuit 140 is normal. Therefore, it is possible to prevent a malfunction due to the erroneous detection of a monitoring unit.

(Initial Diagnosis by Magnetization Signal Monitoring Unit 162)

An initial diagnostic method for the magnetization signal monitoring unit 162 will be explained below in detail.

FIG. 6 is a view illustrative of a configuration of the magnetization signal monitoring unit 162. Herein, parts corresponding to the monitoring block and the AND circuit in FIG. 4 are illustrated.

The magnetization signal monitoring unit 162 monitors a waveform of a magnetization signal. In the regular diagnostic mode, a magnetization signal output from the magnetization waveform generating unit 144 is input to an input terminal 162 a as a regular signal. Moreover, in the initial diagnostic normal mode, a magnetization signal with an ideal waveform is input to the input terminal 162 a as a normal signal for the initial diagnosis. On the other hand, in the initial diagnostic abnormal mode, a magnetization signal with a frequency different from the above-mentioned normal signal (e.g., ½ frequency) is input to the input terminal 162 a as an abnormal signal for the initial diagnosis.

FIG. 7A and FIG. 7B are graphs of signal waveforms for the initial diagnosis. FIG. 7A illustrates a normal signal, while FIG. 7B illustrates an abnormal signal. The magnetization signal monitoring unit 62 counts periods of time T1 and T2, and then compares them to respective predetermined normal values, so as to diagnose. The period of time T1 denotes a period from when a target monitored signal becomes equal to or greater than a threshold V1 to when it becomes equal to or less than a threshold V2. The period of time T2 denotes a period from when it becomes equal to or less than the threshold V2 to when it becomes equal to or greater than the threshold V1. Herein, the threshold V1 is set to 4.25 V, and the threshold V2 is set to 0.75 V, for example.

That is, as illustrated in FIG. 7A and FIG. 7B, the signal input to the input terminal 162 a is then input to comparators 162 b and 162 c. The comparator 162 b compares the input signal to the threshold V1, and when the input signal is equal to or greater than the threshold V1, a high level signal is output. Moreover, the comparator 162 c compares the input signal to the threshold V2, and when the input signal is equal to or less than the threshold V2, it outputs a high level signal. Output signals from the comparators 162 b, and 162 c are input to counter circuits 162 d and 162 e, respectively.

The counter circuit 162 d counts the period of time T1 from when the input signal becomes equal to or greater than the threshold V1 to when it becomes equal to or less than the threshold V2, based on the output signals from the comparators 162 b and 162 c, and then outputs the result to a comparator 162 f. Moreover, a counter circuit 162 e counts the period of time T2 from when the input signal becomes equal to or less than the threshold V2 to when it becomes equal to or greater than the threshold V1, based on the output signals from the comparators 162 b and 162 c, and then outputs the result to a comparator 162 g.

The comparator 162 f compares the period T1 to a normal value T0, and when the counted period T1 differs from the normal value T0, a signal of “1” is output. Similarly, the comparator 162 g compares the period T2 to the normal value T0, and when the counted period T2 differs from the normal value T0, the signal of “1” is output. Output signals from the comparators 162 f and 162 g are then input to an OR circuit 162 h. An output from the OR circuit 162 h is latched by a latch circuit 162 i, and input to an AND circuit 162 k at a timing specified by a determination timing generating unit 162 j.

With such a configuration, the initial diagnostic process of FIG. 5 mentioned above is carried out. Once the flag mask OFF (i.e., 1) is input to the AND circuit 162 k of the magnetization signal monitoring unit 162, the normal signal illustrated in FIG. 7A is input from the input terminal 162 a, to begin with. In this situation, when the monitoring block is functioning normally, the period of time T1 and the period of time T2 are equal to the normal value T0. The period of time T1 is a period from when the input signal becomes equal to or greater than the threshold V1 to when it becomes equal to or less than the threshold V2, and the period of time T2 is a period from when the input signal becomes equal to or less than the threshold V2 to when it becomes equal to or greater than the threshold V1. Therefore, the output from the latch circuit 162 i becomes “0”, and the output from the AND circuit 162 k also becomes “0”.

On the other hand, when the monitoring block is not functioning normally, the period of time T1 and the period of time T2 differ from the normal value T0. The period of time T1 is a period from when the input signal becomes equal to or greater than the threshold V1 to when it becomes equal to or less than the threshold V2, and the period of time T2 is a period from when the input signal becomes equal to or less than the threshold V2 to when it becomes equal to or greater than the threshold V1. Therefore, the output from the latch circuit 162 i becomes “1”, and the output from the AND circuit 162 k also becomes “1.”

In this manner, diagnosis is firstly conducted in the initial diagnostic normal mode, and then it is determined whether it is diagnosed as normal correctly (i.e., whether the output from the AND circuit 162 k is “0”) when a normal signal is input. At this time, when the output from the AND circuit 162 k is not “0”, it is determined that the magnetization signal monitoring unit 162 is not functioning normally.

When the output from the AND circuit 162 k is “0” at the time of inputting the normal signal, and it is determined that the magnetization signal monitoring unit 162 is functioning normally, it is then diagnosed in the initial diagnostic abnormal mode. In this case, the abnormal signal illustrated in FIG. 7 b is input from the input terminal 162 a. At this time, when the monitoring block is functioning normally, the period of time T1 and the period T2 differ from the normal value T0. The period of time T1 is a period from when the input signal becomes equal to or greater than the threshold V1 to when it becomes equal to or less than the threshold V2, and the period of time T2 is a period from when the input signal becomes equal to or less than the threshold V2 to when it becomes equal to or greater than the threshold V1. Therefore, the output from the latch circuit 162 i becomes “1”, and the output from the AND circuit 162 k also becomes “1”.

On the other hand, when the monitoring block is not functioning normally, in some cases, the period of time T1 and the period of time T2 equals the normal value. The period of time T1 is a period from when the input signal becomes equal to or greater than the threshold V1 to when it becomes equal to or less than the threshold V2. The period of time T2 is a period from when the input signal becomes equal to or less than the threshold V2 to when it becomes equal to or greater than the threshold V1. In such a case, the output from the latch circuit 162 i becomes “0”, and the output from the AND circuit 162 k also becomes “0.”

In this manner, diagnosis in the initial diagnostic normal mode is conducted followed by diagnosis in the initial diagnostic abnormal mode, and it is determined whether it is correctly diagnosed as abnormal (i.e., whether the output from the AND circuit 162 k is “1”) when an abnormal signal is input. At this time, when the output from the AND circuit 162 k is not “1”, it is determined that the magnetization signal monitoring unit 162 is not functioning normally.

Moreover, when the output from the AND circuit 162 k is “1” when this abnormal signal is input, and it is determined that the magnetization signal monitoring unit 162 is functioning normally, diagnosis in the initial diagnostic normal mode is conducted again. That is, the normal signal illustrated in FIG. 7A is input from the input terminal 162 a again, and it is confirmed whether to be diagnosed as normal correctly (i.e., whether the output from the AND circuit 162 k is “0”). At this time, when switching of input signals for the initial diagnosis is performed normally, and the magnetization signal monitoring unit 162 is functioning normally, it is diagnosed as normal correctly. On the other hand, when switching of input signals for the initial diagnosis is not performed normally, diagnosis is not carried out normally even when the magnetization signal monitoring unit 162 is functioning normally. Accordingly, the initial diagnosis by inputting a normal signal, an abnormal signal, and then the same normal signal again, allows confirmation that the initial diagnostic function is operating normally.

As described above, as a magnetization signal monitoring method, there are provided the threshold V1 lower than the maximum value of a target monitored signal, and the threshold V2 higher than the minimum value of a target monitored signal (<V1). The method is employed such that the period of time T1 from when the input signal becomes equal to or greater than the threshold V1 to when it becomes equal to or less than the threshold V2, and the period of time T2 from when the input signal becomes equal to or less than the threshold V2 to when it becomes equal to or greater than the threshold V1 are equal to the normal value, respectively. A signal with a frequency different from that of the normal signal is used as an abnormal signal for the initial diagnosis. In this manner, by the use of an abnormal signal with a frequency different from that of the normal signal, the above-mentioned periods T1 and T2 in the case where the abnormal signal is used as a target monitored signal are made to differ from the normal value. Therefore, it is possible to determine appropriately whether the magnetization signal monitoring unit 162 is functioning normally, using those signals.

Moreover, the abnormal signal for the initial diagnosis can be generated by using a half frequency outputting function of a magnetization pulse generating function. In this manner, it is possible to generate a suitable abnormal signal relatively easily.

(Initial Diagnosis of Phase Monitoring Unit 163)

An initial diagnostic method of the phase monitoring unit 163 will be explained below in detail.

FIG. 8 is a block diagram illustrative of a configuration of the phase monitoring unit 163. Herein, only a part corresponding to the monitoring block in FIG. 4 is illustrated.

The phase monitoring unit 163 monitors a difference in phase between the torque detecting signal and the magnetization signal in the regular diagnostic mode. Regarding a coil-type torque sensor, in particular, when an abnormality occurs in the coil sensor unit, the torque detecting signal may shift its phase from the magnetization signal. When the phase of the magnetization signal shifts from that of the torque detecting signal and the torque detecting signal has an amplitude equal to or greater than a certain fixed value, it is determined that an abnormality has occurred in the torque detecting signal.

That is, as illustrated in FIG. 8, the monitoring block includes three comparators 163 a to 163 c, and an AND circuit 163 d to which outputs from the comparators 163 a to 163 c are input. The comparator 163 a compares the magnetization signal input from an input terminal 163 e to a threshold V3. When the magnetization signal is equal to or greater than the threshold V3, a high level signal is output. Moreover, the comparator 163 b compares the magnetization signal input from the input terminal 163 e to a threshold V4. When the magnetization signal is equal to or smaller than the threshold V4, a high level signal is output.

Furthermore, the comparator 163 c compares the monitored signal to the threshold V3. When the monitored signal is equal to or smaller than the threshold V3, a high level signal is output. In the regular diagnostic mode, the torque detecting signal is input to the comparator 163 c as a monitored signal (i.e., a switch SW4 is turned on). Moreover, in the initial diagnostic normal mode, the normal signal for the initial diagnosis is used as a monitored signal and the magnetization signal is input to the comparator 163 c as the normal signal (i.e., a switch SW5 is turned on). Then, in the initial diagnostic abnormal mode, the abnormal signal for initial diagnosis is used as a monitored signal and a signal via a phase shift circuit 163 f subjected to the phase shifting of the magnetization signal is input to the comparator 163 c as the abnormal signal (i.e., a switch SW6 is turned on). The phase shift circuit 163 f is a circuit for shifting the phase of the magnetization signal by 90 degrees and is constituted by an operational amplifier, for example.

Note that the thresholds V3and V4 are set to fall between the minimum amplitude value and the maximum amplitude value of the magnetization signal, respectively, where V3<V4 is satisfied. Herein, the threshold V3is set to 1.75 V, and the threshold V4 is set to 2.75 V, for example.

Furthermore, herein, the case where the phase difference between the normal signal (magnetization signal) and the abnormal signal is 90 degrees is explained. However, it may take a value other than 90 degrees.

Moreover, the period at high level of the output from the AND circuit 163 d is counted and the counted value is then compared to a normal value. When the period at high level is equal to or higher than the normal value, a signal of “1” indicating an abnormality of the torque detecting signal, is input to a circuit corresponding to the AND circuit of FIG. 4.

With such a configuration, the switch SW4 turns on and the torque detecting signal is input to the comparator 163 c in the regular diagnostic mode. At this time, when the torque detecting signal is normal where its phase is not shifted from that of the magnetization signal, the output from the AND circuit 163 d is “0”. An operation when it is normal will be explained in detail hereinafter.

As illustrated in FIG. 9A, an output (CP1 output) from the comparator 163 a is at a high level only during a period when a magnetization signal a is equal to or higher than the threshold V3. Moreover, an output (CP2 output) from the comparator 163 b is at a high level only during a period when the magnetization signal a is equal to or lower than the threshold V4. Furthermore, an output (CP3 output) from the comparator 163 c is at a high level only during a period when a monitored signal (i.e., torque detecting signal b) is equal to or lower than the threshold V3. Therefore, when the torque detecting signal b is normal where its phase is not shifted from that of the magnetization signal a, there is no period in which all of the three outputs CP1 to CP3 are at a high level at the same time, as illustrated at the bottom in FIG. 9A. Therefore, the output from the AND circuit 163 d is always “0” and the torque detecting signal b is determined to be normal.

On the other hand, when such an abnormality that the torque detecting signal has its shifted phase from that of the magnetization signal, there is a period in which the output from the AND circuit 163 d is at a high level. As illustrated in FIG. 9B, when the monitored signal (i.e., torque detecting signal b′) has a phase shifted by 90 degrees from that of the magnetization signal a, the output (CP3 output) from the comparator 163 c is at a high level at a different timing from that in the normal mode. In this case, there is a period in which all of the outputs CP1 to P3 from the three comparators 163 a to 163 c are at a high level. As illustrated in region a of the bottom in FIG. 9B, there is a period in which the output from the AND circuit 163 d is at a high level. When this period is determined to be equal to or higher than a normal value, it is determined that an abnormality has occurred in the torque detecting signal b′.

By monitoring the output from the AND circuit 163 d in such a manner, it is possible to determine whether the monitored signal has a phase shifted from that of the magnetization signal appropriately.

Once the aforementioned initial diagnostic process in FIG. 5 is performed and a flag mask OFF (i.e., 1) is input to the phase monitoring unit 163, first of all, the switch SW5 in FIG. 8 turns on and a magnetization signal is input to the comparator 163 c as a normal signal for the initial diagnosis. That is, the magnetization signal serves as a monitored signal. Naturally, since the monitored signal has the same phase with that of the magnetization signal, the output from the AND circuit 163 d is always “0” as long as the monitoring block is functioning normally.

On the other hand, when the monitoring block is not functioning normally, it will be misunderstood that the monitored signal shifts its phase from that of the magnetization signal. Thus, there is a period in which the output from the AND circuit 163 d is at a high level.

In this manner, diagnosis is firstly conducted in the initial diagnostic normal mode to confirm whether the normal signal (magnetization signal) is diagnosed as normal correctly when it is input (i.e., whether the output from the AND circuit 163 d is always “0”). At this time, when the output from the AND circuit 163 d is not always “0”, it is determined that the phase monitoring unit 163 is not functioning normally.

When this normal signal is received, the output from the AND circuit 163 d is always “0”, and when it is determined that the phase monitoring unit 163 is functioning normally, diagnosis will then be conducted in the initial diagnostic abnormal mode. In this case, the switch SW6 in FIG. 8 is turned onto input to the comparator 163 c a signal having a phase shifted from that of the magnetization signal, as an abnormal signal for the initial diagnosis. At this time, since the target monitored signal has a different phase from that of the magnetization signal, there is a high level period in the output from the AND circuit 163 d as long as the monitoring block is functioning normally.

On the other hand, in the case where the monitoring block is not functioning normally, it is misunderstood that the target monitored signal has the same phase with that of the magnetization signal, thereby making the output from the AND circuit 163 d always “0”.

In such a manner, the diagnosis in the initial diagnostic normal mode is conducted followed by diagnosis in the initial diagnostic abnormal mode. Once an abnormal signal is input, it is determined whether an abnormality is diagnosed correctly (i.e., whether the output from the AND circuit 163 d is at a high level). At this time, when the output from the AND circuit 163 d is always “0”, it will be determined that the phase monitoring unit 163 is not functioning normally.

When there is a high level period in the output from the AND circuit 163 d at the time of inputting the abnormal signal and it is thus determined that the phase monitoring unit 163 is functioning normally, the diagnosis is conducted again in the initial diagnostic normal mode. That is, the switch SW5 of FIG. 8 is turned on, a magnetization signal is input to the comparator 163 c again as a normal signal for the initial diagnosis to confirm whether it is diagnosed as normal correctly (whether the output from the AND circuit 163 d is always “0”).

As mentioned above, as a phase monitoring method, there are provided three comparators 163 a to 163 c, each of which outputs a high level value within a period in which the magnetization signal is equal to or higher than the threshold V3, a period in which the magnetization signal is equal to or lower than the threshold V4, and a period in which the monitored signal is equal to or lower than the threshold V3, to determine whether all of the outputs from the three comparators 163 a to 163 c falling within a high level period are equal to a normal value or greater respectively at the same time. A signal with a different phase from that of the normal signal is used as the abnormal signal for the initial diagnosis. By the use of the signal with a phase different from that of the normal signal in such a manner, it is possible to generate a period in which all the outputs from the three comparators 163 a to 163 c are at a high level at the same time, when the abnormal signal is used as a target monitored signal.

At this time, phase difference is set to 90 degrees between the normal signal and the abnormal signal when the abnormal signal is used as a monitored signal. This makes it possible to set all of the outputs from the three comparators 163 a to 163 c within a high level period at a normal value or greater with certainty. Therefore, the use of such a signal allows appropriate determination of whether the phase monitoring unit 163 is functioning normally. Moreover, a suitable abnormal signal is obtainable relatively easily by shifting the phase of the normal signal via the phase shift circuit.

(Initial Diagnosis of MUX/ADC Monitoring Unit 165)

An initial diagnostic method of a MUX/ADC monitoring unit 165 will be explained now in detail.

FIG. 10 is a block diagram of a configuration of the MUX/ADC monitoring unit 165. Herein, only a part corresponding to the monitoring block in FIG. 4 is illustrated.

The MUX/ADC monitoring unit 165 determines that an abnormality has occurred in the MUX and the ADC, and outputs a signal of “1”, when the ADC output value differs from an expected value. Herein, multiple voltages (VCC*1/2, VCC*1/3, VCC*2/3, VCC*3/3, and VCC*0/3) in a regularly used region (0 to VCC) are used as monitored signals, and ADC output values thereof are compared to respective expected values.

That is, as illustrated in FIG. 10, the monitoring block is provided with an MUX 165 a and an ADC 165 b. In the regular diagnostic mode, VCC*1/3, VCC*2/3, VCC*1/2, VCC*3/3, and VCC*0/3, in addition to a main torque value and a sub torque value, are input to the MUX 165 a. The MUX 165 a chooses these signals successively according to an Mux selection signal to output to an ADC 165 b. The ADC 165 b carries out A/D conversion of a signal input from the MUX 165 a to output to a latch circuit 165 c corresponding to the input signal.

The main torque value and sub torque value latched by the latch circuit 165 c are output to the communication output circuit 154 mentioned above. On the other hand, the ADC output value for each input voltage latched by the latch circuit 165 c is then output to a comparator 165 d. The comparator 165 d compares each ADC output value to an expected value, and the result thereof is then output to an OR circuit 165 e. The output from the OR circuit 165 e is “1” when at least one of the ADC output values is “1.” The output from the OR circuit 165 e is latched by a latch circuit 165 f, and then input to a circuit corresponding to the AND circuit in FIG. 4 at a timing specified by a determination timing generating unit 165 g.

In the initial diagnostic normal mode, as a normal signal for initial diagnosis, voltage values (VCC*1/3, VCC*2/3, VCC*1/2, VCC*3/3, and VCC*0/3) equal to those in the regular diagnostic mode are input to respective input terminals of the MUX 165 a, and the ADC output value is monitored using these voltage values as monitored signals.

On the other hand, in the initial diagnostic abnormality mode, a voltage value different from that in the regular diagnostic mode is input as an abnormal signal for the initial diagnosis to each input terminal of the MUX 165 a, and the ADC output value is monitored using these voltage values as monitored signals.

That is, switches SW7 to SW11, each being switchable according to an input signal selecting instruction, are provided on the previous stage of the MUX 165 a, as an abnormality generating circuit. Herein, the input signal selecting instruction is an instruction signal, which makes each lower switch turn on in the regular diagnostic mode and in the initial diagnostic normal mode, and makes each upper switch turn on in the initial diagnostic abnormal mode.

With such a configuration, in the initial diagnostic abnormality mode, VCC*1/3 and VCC*2/3, and VCC*3/3 and VCC*0/3 are input to the MUX 165 a alternately, and VCC*2/3 is input from the input terminal of VCC*1/2. Therefore, when the ADC output value is monitored in this mode, the output value from the comparator 165 d is “1” indicating abnormality, and thus the output from the OR circuit 165 e is also “1” indicating abnormality.

When the torque output is zero (i.e., a neutral value), the torque output value is equal to 1/2 VCC. Moreover, even when an abnormality occurs in the MUX 165 a or the ADC 165 b, the ADC output value will be the same value as the neutral value. Therefore, when an abnormality occurs in the MUX 165 a or the ADC 165 b, there is a possibility that it is erroneously detected as in a neutral mode even when the torque output is made in actuality. Moreover, in the initial diagnosis, when only 1/2 VCC is used as a normal signal and even when an abnormality occurs in the MUX 165 a or the ADC 165 b, normality will be determined erroneously.

Therefore, in the present embodiment, an initial diagnosis is conducted in a regularly used region, such as not only 1/2 VCC but also 1/3 VCC or 2/3 VCC. This allows appropriate diagnosis of whether or not the MUX/ADC monitoring unit 165 is functioning normally. Therefore, it is possible to prevent an erroneous detection to be in the neutral mode, although the torque output is made in actuality.

As mentioned above, immediately after the power is turned on but before the ECU side starts control, the initial diagnosis of the monitoring unit itself for monitoring the signal processing circuit 140 is conducted. The confirmation that normal operations of all of the monitoring units is notified to the ECU side, so that the torque sensor 20 then starts its operation and the ECU side starts its steering auxiliary control. As a result, the reliability of the monitoring units can be improved, and erroneous detection by the monitoring units can be suppressed. This allows the steering auxiliary control with the use of the torque detecting device 30 with high reliability, thereby enhancing stability and reliability of the control.

Moreover, as an initial diagnostic method of the monitoring units, there is provided a method of inputting a normal signal and an abnormal signal alternately, diagnosing the normality when the normal signal is input, and determining that an abnormality is diagnosed at the time of inputting an abnormal signal. It is therefore possible to determine whether the monitoring units are operating normally appropriately. Furthermore, after the normal signal and the abnormal signal are input, the normal signal is input again for the initial diagnosis. Therefore, it is possible to determine whether the initial diagnostic function is operating normally, such as whether switching of the input signals for the initial diagnosis is carried out normally, appropriately.

(Modifications to the Embodiment)

Note that in the case where a redundant system, such as a backup function, is included in the aforementioned first embodiment, a select function for preventing adoption of a system in which an abnormality has occurred can be arranged.

(Second Embodiment)

A second embodiment according to the present invention is described below.

The second embodiment differs in the configuration of the torque detecting device 30 from the first embodiment mentioned above.

FIG. 11 is a block diagram of a configuration of the torque detecting device 30. The torque detecting device 30 is provided with the torque sensor 20 mentioned above. The torque sensor 20 is provided with two sets of coil pairs 22A and 22B. Moreover, as illustrated in the peripheral configuration of the coil of FIG. 12, the torque sensor 20 includes: a first yoke 81A; a second yoke 81B; the cylinder member 83; the multiple windows 831, which are arranged in an outer peripheral part of the cylinder member 83, facing the coil pairs 22A and 22B; the torsion bar 84; and the sensor shaft 85. Note that the torsion bar 84, the sensor shaft 85, and the input shaft 2 a and output shaft 2 b of the steering shaft 2 are arranged coaxially.

The coil pair (first coil pair) 22A include coils 22Aa and 22Ab in conformity with the same standard, and is arranged in the cylindrical first yoke 81A, as illustrated in FIG. 12. Similarly, the coil pair (second coil pair) 22B include coils 22Ba and 22Bb in conformity with the same standard, and is arranged in the cylindrical second yoke 81B, as illustrated in FIG. 12.

The torque detecting device 30 is arranged for the first and the second coil pair 22A and 22B, respectively, and has signal processing circuits (signal processing units) 59A and 59B for processing the output signals from the respective coil pairs. The signal processing circuits 59A and 59B are arranged in the controller 15.

Moreover, the torque detecting device 30 includes clock signal generating circuits (CLK) 62A and 62B, each outputting a clock signal to be a source of sinusoidal waves generated by magnetization signal generating units 60A and 60B. The clock signals generated by the clock signal generating circuits 62A and 62B are supplied to the magnetization signal generating units 60A and 60B, respectively.

Herein, each of the clock signal generating circuits 62A and 62B uses an inexpensive clock oscillator, such as a CR oscillator, for example. This CR oscillator may generate a frequency fluctuation exceeding a tolerant frequency range (e.g., +−20%).

Therefore, abnormality detectors 64A and 64B are needed for detecting whether the frequency fluctuation of each of the clock signals generated by the clock signal generating circuits 62A and 62B falls within a tolerant range.

As illustrated in FIG. 13, each of the abnormality detectors 64A and 64B includes: a low-pass filter (a monitoring low-pass filter) 68, to which sine wave signals output from the magnetization signal generating units 60A and 60B are supplied; and a clock frequency fluctuation monitoring unit 69 for detecting fluctuation of amplitude of a filter output VF from the low-pass filter 68, and detecting fluctuation of amplitude of each of the clock signals.

The low-pass filter 68 includes a resistor R1 and a capacitor C1. A cutoff frequency fc of the low-pass filter 68 is set to a value in the vicinity of 6 kHz, for example, to attenuate each of the sine wave signals based on respective clock signals with a set frequency of 9 kHz. The reason why the cutoff frequency fc of the low-pass filter 68 is set to the value in vicinity of 6 kHz is that for example, when a frequency fluctuation range from +−20% with respect to 9 kHz magnetization signal is monitored, a relationship between the cutoff frequency fc of the first-order low-pass filter 68 and the difference in voltage from the peak value at 9 kHz is illustrated in FIG. 14. That is, as indicated by a characteristic curve L1, the difference in voltage at 5895 Hz is a peak value within the range between 9 kHz and 7.2 kHz, which is −20% of 9 kHz. On the other hand, as indicated b a characteristic curve L2, the difference in voltage at 6631 Hz is a peak value within the range between 9 kHz and 10.8 kHz, which is +20% of 9 kHz. Therefore, 6 kHz, which is approximately a middle value between the peak along the characteristic curve L1 and that along the characteristic curve L2, is chosen as the cutoff frequency fc of the low-pass filter 68 for monitoring the frequency fluctuation range of +−20%. Thereby, it is possible to replace the frequency fluctuation with the amplitude fluctuation efficiently.

As illustrated in FIG. 15A to FIG. 15D, by the low-pass filter 68 attenuating the magnetization signal of a sinusoidal wave with a high frequency in this manner, the frequency fluctuation of the clock signal of the filter output VF from the low-pass filter 68 is represented as the amplitude fluctuation. That is, as illustrated in FIG. 15B, when tolerance for frequency fluctuation of the clock signal is set to the range of +−20% and the frequency fluctuation of the clock signal falls within +−20%, as illustrated in FIG. 15B, the peak value along the upper half wave of the filter output VF falls within the range of an upper-limit voltage setting value VH (e.g., 3.87V) and a lower-limit voltage setting value VL (e.g., 3.55 V). On the other hand, as illustrated in FIG. 15C, in the case where the frequency of the clock signal is lower by 20% or more than a reference frequency fb (i.e., fb−fb×20%), the peak value along the filter output VF is determined to be abnormal, because it exceeds the upper-limit voltage setting value VH. On the contrary, as illustrated in FIG. 15D, in the case where the frequency of the clock signal is higher by 20% or more than the reference frequency fb (i.e., fb−fb×20%), the peak value along the filter output VF is determined to be abnormal because it is lower than a lower-limit voltage setting value VL.

Therefore, the clock frequency fluctuation monitoring unit 69 determines whether or not the peak voltage of the filter output VF from the low-pass filter 68 falls within a normal range between the upper-limit voltage setting value VH and the lower-limit voltage setting value VL, so that whether or not the frequency fluctuation of the clock signal falls within a tolerance can be detected correctly.

Therefore, as illustrated in FIG. 13, the clock frequency fluctuation monitoring unit 69 includes a window comparator 69 a and a logic circuit 69 b connected to the output side of the window comparator 69 a.

The window comparator 69 a includes a voltage divider VD for dividing a direct current power source, and two comparators CP1 and CP2. The voltage divider VD has three resistors R1, R2, and R3 connected in series between a direct current power source terminal VDD and a grounded terminal. The upper-limit voltage setting value VH mentioned above is obtained at a junction point of the resistors R1 and R2, and the lower-limit voltage setting value VL mentioned above is obtained at a junction point of the resistors R2 and R3.

The filter output VF from the low-pass filter 68 is input to a non-inverting input terminal of the comparator CP1, and the upper-limit voltage setting value VH output from the voltage divider VD is input to an inverting input terminal thereof. Moreover, the filter output VF from the low-pass filter 68 is input to the inverting input terminal of the comparator CP2, and the lower-limit voltage setting voltage VL output from the voltage divider VD is input to the non-inverting input terminal.

Therefore, as illustrated in FIG. 15B, regarding the window comparator 69 a, when the peak value along the upper half wave of the filter output VF falls within a normal voltage range between the upper-limit voltage setting value VH and the lower-limit voltage setting value VL, the output signal Scp1 from the comparator CP1 is at a low level while the filter output VF exceeds the lower-limit voltage setting voltage VL, and the output signal Scp2 from the comparator CP2 is at a high level since filter output VF is less than the upper-limit voltage setting value VH.

Moreover, as illustrated in FIG. 15 c, in the case where the peak value along the upper half wave of the filter output VF exceeds the upper-limit voltage setting value VH, the output signal Scp1 from the comparator CP1 is at a high level while the filter output VF exceeds the upper-limit voltage setting value VH. The output signal Scp2 from the comparator CP2 is also at a high level while the filter output VF exceeds the lower-limit voltage setting value VL.

Furthermore, as illustrated in FIG. 15D, when the peak value along the upper part half wave of the filter output VF is lower than the upper-limit voltage setting value VH, both of the output signal Scp1 of the comparator CP1 and the output signal Scp1 of the comparator CP2 maintain a low level.

Therefore, when the frequency component of the clock signal falls within a normal range, the output signal Scp1 of the comparator CP1 is at a low level, whereas the output signal Scp2 of the comparator CP2 is at a high level.

The logic circuit 69 b includes a NAND gate NG1 for receiving the output signal Scp1 of the comparator CP1 at two input terminals thereof, and a NAND gate NG2 for receiving the output signal from the NAND gate NG1 and the output signal Scp2 of the comparator CP2 at two input terminals thereof.

Therefore, in the logic circuit 69 b, a low level detection signal is output from the NAND gate NG2, when the frequency component of the clock signal falls within the normal range. On the contrary, a high level detection signal is output from the NAND gate NG2 when the frequency fluctuation is large, such that the frequency component of the clock signal is lower or higher than the normal range, that is, when it is found abnormal.

Meanwhile, ones of terminals of the coils 22Aa and 22Ab constituting the first coil pair 22A are connected to the magnetization signal generating unit 60A via the resistors 61Aa and 61Ab, respectively. The other terminals of the coils 22Aa and 22Ab constituting the first coil pair 22A are grounded. A bridge circuit is thus configured with the coils 22Aa and 22Ab and the resistors 61Aa and 61Ab.

Similarly, ones of terminals of the coils 22Ba and 22Bb constituting the second coil pair 22B are connected to the magnetization signal generating unit 60B via the resistors 61Ba and 61Bb, respectively. On the other hand, the other terminals of the coils 22Ba and 22Bb constituting the second coil pair 22B are grounded. A bridge circuit is thus configured with the coils 22Ba and 22Bb and the resistors 61Ba and 61Bb.

The output signals from the first coil pair 22A that are differential signals from the bridge circuit are output to the signal processing circuit 59A. The output signals from the second coil pair 22B that are differential signals from the bridge circuit are output to the signal processing circuit 59B.

The signal processing circuit 59A includes a differential amplifier 51A, a rectifying and smoothing circuit 52A, and a noise rejecting filter 54A. Moreover, the signal processing circuit 59B includes a differential amplifier 51B, a rectifying and smoothing circuit 52B, and a noise rejecting filter 54B.

The differential amplifier 51A amplifies output difference between the coils 22Aa and 22Ab constituting the first coil pair 22A, that is, the difference (terminal voltage difference) between the terminal voltages of the coils 22Aa and 22Ab, and then outputs the amplified value. The rectifying and smoothing circuit 52A rectifies and smoothes the output from differential amplifier 51A, and then outputs the resulting value. The output from the rectifying and smoothing circuit 52A passes through the noise rejecting filter 54A to remove a noise, and the resulting value is input to a torque calculation unit 56A.

Note that since the signal processing circuit 59B has the same configuration as the signal processing circuit 59A, the description thereof will be omitted.

Moreover, torque calculation units 56A and 56B calculate through a predetermined operation, the steering torque generated in the steering system based on the outputs (e.g., an average value) from the noise rejecting filters 54A and 54B. A motor control unit 57 is provided in the ECU, and supplies to the electric motor 12, a drive current for generating a steering auxiliary torque that reduces the steering torque given by a driver, based on the calculated results of the torque calculation units 56A and 56B.

The torque detecting device 30 has a redundant configuration including: a first torque detecting system having the first coil pair 22A and the signal processing circuit 59A; and a second torque detecting system having the second coil pair 22B and the signal processing circuit 59B. The electric power steering device illustrated in FIG. 1 usually controls the electric motor 12 for the steering auxiliary control, based on a steering torque detected by the first torque detecting system and the second torque detecting system. On the other hand, when a malfunction occurs in the first or the second torque detecting system, switching to a malfunction-free system will be made to continue detection of the steering torque and continue the steering auxiliary control.

Moreover, since an abnormality of the steering torque detecting function will adversely affect the steering auxiliary control seriously, the aforementioned abnormality detectors 64A and 64B regularly monitor whether there is an abnormality in frequency fluctuation of the clock signal while the controller 15 is conducting the steering auxiliary control.

As mentioned above, the abnormality detectors 64A and 64B each include a clock frequency fluctuation monitoring unit 69 provided with the low-pass filter 68 and the window comparator 69 a. The clock frequency fluctuation monitoring unit 69 detects a frequency fluctuation of the clock signal as an amplitude fluctuation of the filter output VF from the low-pass filter 68. When the clock frequency is normal, the output signal output from the clock frequency fluctuation monitoring unit 69 is at a low level. When the clock frequency deviates from a normal range, the output signal output from the clock frequency fluctuation monitoring unit 69 is at a high level.

In general, in order to monitor the accuracy of the clock frequency, there is a technique of providing independently a clock signal generating circuit for monitoring the correctness of the clock frequency based on difference therebetween. However, in the case of using this technique, a high-accuracy clock is needed as a clock for monitoring to monitor the accuracy of the clock frequency of each of the clock signal generating circuits 62A and 62B. This increases the costs, and when an abnormality occurs in the high-accuracy clock signal generating circuit, the abnormality cannot be detected.

Meanwhile, in the present embodiment, an inexpensive CR oscillator is applicable to the clock signal generating circuits 62A and 62B. In this case, monitoring of the clock frequency is possible using the clock frequency fluctuation monitoring unit 69 including the low-pass filter 68 and the window comparator 69 a. Therefore, this eliminates the necessity of an expensive clock signal generating circuit independently for monitoring. Consequently, the cost can be reduced by that much.

Note that in the second embodiment, the case where the low-pass filter 68 has a first-order filter configuration including a resistor R0 and a capacitor C0 has been described. The present invention, however, is not limited to this configuration. A second-order or higher-filter configuration can be employed to improve the attenuation characteristics as illustrated in FIG. 15A. In addition, it is possible to improve the degree of freedom for design values for amplitude fluctuation of the filter output VF due to frequency fluctuation and accuracy of the elements constituting the low-pass filter.

Moreover, as illustrated in FIG. 16, the abnormality detectors 64A and 64B include monitoring unit diagnosing units 71A and 71B, respectively, each having an initial diagnostic function for diagnosing whether the clock frequency fluctuation monitoring unit 69 is operating normally.

This initial diagnosis starts immediately after the power of the controller 15 is turned on (i.e., immediately after the ignition switch 18 is turned on) and before the controller 15 starts the steering auxiliary control. Note that the controller 15 is prevented from using the torque sensor signal during the initial diagnosis (i.e., the steering auxiliary control is prohibited) due to a set flag, etc.

As illustrated in FIG. 16, the monitoring unit diagnosing unit 71A (or 71B) includes a clock frequency selecting circuit 72A (or 72B) between the clock signal generating circuit 62A (or 62B) and the magnetization signal generating unit 60A (or 60B). The clock frequency selecting circuit 72A (or 72B) includes: three switches SWa, SWb, and SWc with one ends connected to the clock signal generating circuit 62A (or 62B); and frequency dividers 73 a, 73 b, and 73 c connected to the other respective ends of the switches SWa, SWb, and SWc. Clock signals output from the frequency dividers 73 a, 73 b, and 73 c are input to the magnetization signal generating unit 60A (or 60B).

Herein, the frequency divider 73 a generates a regular clock signal CPu with the aforementioned reference frequency fb of 9 kHz to be used usually. Moreover, the frequency divider 73 b generates an abnormally low frequency clock signal CPaL set at a frequency lower than the acceptable lower-limit range (−20%), which is usually lower than the regular clock signal CPu. Furthermore, the frequency divider 73 c generates an abnormally high frequency clock signal CPaH set at a frequency higher than the acceptable upper-limit range (+200), which is usually higher than the regular clock signal CPu.

Moreover, the monitoring unit diagnosing unit 71A (or 71B) includes comparators CP1 and CP2 of the window comparator 69 a of the clock frequency fluctuation monitoring unit 69. A predetermined high voltage V1 illustrated in FIG. 15B is input to the comparator CP1, where the predetermined high voltage V1 is lower than the peak value (which is lower than the upper-limit voltage setting value VH) along the upper half wave of the filter output VF output from the low-pass filter 68 and higher than the lower-limit voltage setting value VL. The filter output VF originates from a sinusoidal wave obtained by the magnetization signal generating units 60A and 60B converting the aforementioned abnormally low-frequency clock signal CPaL. On the other hand, a predetermined low voltage V2 illustrated in FIG. 15B is input to the comparator CP1, where the predetermined low voltage V2 is higher than the peak value along the lower half wave of the filter output VF output from the low-pass filter 68. The filter output VF originates from a sinusoidal wave obtained by the magnetization signal generating units 60A and 60B converting the aforementioned abnormally high-frequency clock signal CPaH.

A comparison output from the comparator CP1 is input to an upper-half wave diagnostic unit 74U for diagnosing based on the upper amplitude part of the magnetization signal, while a comparison output from the comparator CP2 is input to a lower-half wave diagnostic section 74L for diagnosing based on the lower amplitude part of the magnetization signal.

The upper-half wave diagnostic unit 74U includes: a counter 75U to which the comparison output from the comparator CP1 is input; and the comparator CP1 for counting a high-level period of the clock signal. After the counted value CU of the counter 75U converts the aforementioned abnormally low-frequency clock signal CPaL at the magnetization signal generating unit 60A (or 60B) to a sinusoidal wave, it is input to the comparators CPU1 and CPU2 to which is also input the abnormal clock period T1 having the counted value CU corresponding to period in which the upper-half wave of the filter output VF output from the low-pass filter 68 is the predetermined, high voltage V1.

Herein, the comparator CPU1 outputs a high-level comparison signal when the abnormal clock period T1 is longer than the counted value CU. On the other hand, the comparator CPU2 outputs a high-level comparison signal when the abnormal clock period T1 is shorter than the counted value CU.

The comparison signals output from the comparators CPU1 and CPU2 are supplied to a latch circuit 77U. The latch circuit 77U then latches the comparison signals in accordance with a timing signal supplied from a determination timing generating circuit 78U.

The latched signal, which is latched by the latch circuit 77U, is supplied to an AND gate 79U, to which a mask signal that becomes a high level only at the time of initial diagnosis is input. A normality flag Fn1 is reset to “0” indicating an abnormality, when an output from the AND gate 79U is at a low level. On the contrary, the normality flag Fn1 is set to “1” indicating a normality, when the output from AND gate 79U is at a high level.

The lower-half wave diagnostic unit 74L includes a counter 75L to which the comparison output from the comparator CP2 is input, and which counts the high-level period of the clock signal. After the counted value CL of the counter 75L converts the aforementioned abnormally high-frequency clock signal CPaH at the magnetization signal generating unit 60A (or 60B) to a sinusoidal wave, it is input to comparators CPL1 and CPL2 to which the abnormal clock period T2 or the counted value CL corresponding to a period in which the lower-half wave of the filter output VF from the low-pass filter 68 is smaller than the predetermined low voltage V2 is input.

Herein, the comparator CPL1 outputs a high-level comparison signal when the abnormal clock period T2 is longer than the counted value CL. The comparator CPL2 outputs a high-level comparison signal when the abnormal clock period T2 is shorter than the counting value CL.

The comparison signals output from the comparators CPL1 and CPL2 are supplied to a latch circuit 77L. The latch circuit 77L latches the comparison signals in accordance with a timing signal supplied from the determination timing generating circuit 78L.

The latched signal, which is latched by the latch circuit 77L, is supplied to an AND gate 79L, to which a mask signal becomes a high level only at the time of initial diagnosis is input. A normality flag Fn2 is reset to “0” indicating an abnormality, when the output from the AND gate 79L is at a low level. On the contrary, the normality flag Fn2 is set to “1” indicating a normality, when the output from the AND gate 79L is at a high level.

As illustrated in FIG. 16, in the regular monitoring mode (regular diagnostic mode), the switch SWa is turned on to input a regular clock signal to the magnetization signal generating unit 60A (or 60B) and monitor the frequency fluctuation of the clock signal.

On the other hand, each of the switches SWa to SWc is switched on or off in response to a switching signal at the time of the initial diagnosis, so as to input signals for initial diagnosis to the monitoring unit diagnosing unit 71A (or 71B). In the present embodiment, the normal signal, the abnormal signal, and the normal signal are to be input in this order as signals for the initial diagnosis. The switch SWa is turned on for inputting the normal signal, and the switch SWb is turned on followed by the switch SWc sequentially, when inputting the abnormal signal.

FIG. 17 is a flow chart of initial diagnostic process steps executed by the monitoring unit diagnosing units 71A and 71B. This initial diagnostic process is performed immediately after the power is turned on and before the ECU 15 starts the steering auxiliary control, as mentioned above.

First of all, the monitoring unit diagnosing units 71A and 71B set the flag mask to “OFF (high level)” in Step S11.

In Step S12, the monitoring unit diagnosing units 71A and 71B enter the initial diagnostic normal mode by the clock signal selection sections 72A and 72B selecting the regular clock signal CPu (i.e., the switch SWa in FIG. 16 is turned on), and processing then proceeds to Step S13.

In Step S13, after the monitoring unit diagnosing units 71A and 71B stand by until the initial diagnostic normal mode is stable, they determine whether or not both of the normality flags Fn1 and Fn2 are set to “1” indicating the normal mode.

At this time, when a low-frequency abnormality (or high-frequency abnormality) occurs, the counted value CU (or CL) of the counter 75U (or 75L) is equal to the abnormal clock period T1 (or T2) supplied to the comparators CPU1 and CPU2 (or CPL1 and CPL2) in the upper-half wave diagnostic section 74U (or the lower-half wave diagnostic section 74L). Therefore, the comparison outputs from the comparators CPU1 and CPU2 (or CPL1 and CPL2) are at a low level. Therefore, the low level comparison outputs are latched by the latch circuit 77U (or 77L) in accordance with the timing signal from the determination timing generating circuit 78U (or 78L). As a result, the output from the AND gate 79U (or 79L) is at a low level, and the normality flag Fn1 (or Fn2) is reset to “0” indicating the occurrence of an abnormality.

On the contrary, in the lower-half wave diagnostic section 74L (or 74U), the counting value CL (or CU) of the counter 75L (or 75U) becomes a greater value (or a smaller value) than the abnormal clock period T2 (or T1) supplied to the comparators CPL1 and CPL2 (or CPU1 and CPU2). Accordingly, the comparison output from the comparator CPU1 (or CPL2) is at a high level. Therefore, this high-level comparison output is latched by the latch circuit 77L (or 77U) in accordance with the timing signal from the determination timing generating circuit 78L (or 78U). As a result, the output from the AND gate 79L (or 79U) is at a high level, and the normality flag Fn1 (or Fn2) is set to “1” indicating a normality.

Therefore, since the normality flag Fn1 (or Fn2) is reset to “0” and the normality flag Fn2 (or Fn1) is set to “1”, it is determined that the monitoring function of the clock frequency fluctuation monitoring unit 69 has a high frequency abnormality (or low frequency abnormality). Afterwards, processing proceeds to Step S14. A predetermined abnormality process (e.g., notification of the abnormality by a communication output circuit) is carried out in this step, and then the initial diagnostic process completes.

On the other hand, as both of the normality flags Fn1 and Fn2 of the upper-half wave diagnostic section 74U and the lower-half wave diagnostic section 74L are set to “1”, it is thus determined in Step S13 that no abnormality has occurred and processing then proceeds to Step S15. In this Step, the monitoring unit diagnosing units 71A and 71B switch to the low frequency abnormality mode for initial diagnosis by the clock signal selecting circuits 72A and 72B selecting the abnormally low frequency clock signal CPaL for the initial diagnosis (i.e., the switch SWb in FIG. 16 is turned on).

In Step S16, the monitoring unit diagnosing units 71A and 71B stand by until the low frequency abnormality mode for initial diagnosis becomes stable. Afterwards, they read in the normality flag Fn1 of the lower-half wave diagnostic section 74H, and determine whether or not the normality flag Fn1 is reset to “0” and whether or not an abnormality has occurred. At this time, when the occurrence of an abnormality cannot be confirmed due to the normality flag Fn1 set to “1”, it will be determined that the monitoring function of the clock frequency fluctuation monitoring unit 69 has an abnormality and processing then proceeds to Step S14.

On the other hand, when the normality flag Fn1 is reset to “0” in Step S16 and the occurrence of an abnormality is recognized, processing then proceeds to Step S17. In Step S17, the monitoring unit diagnosing units 71A and 71B switch to the high frequency abnormality mode for the initial diagnosis by the clock signal selecting circuits 72A and 72B selecting the abnormality high frequency clock signal CPaH for the initial diagnosis (i.e., the switch SWc of FIG. 16 is turned on).

In Step S18, the monitoring unit diagnosing units 71A and 71B stand by until the high-frequency abnormality mode for the initial diagnosis become stable, read in the normality flag Fn2 of the upper-half wave diagnostic section 74L, and then determine whether the normality flag Fn2 is reset to “0” and the occurrence of an abnormality is confirmed. At this time, when the normality flag Fn2 is reset to “1” and no occurrence of an abnormality is recognized, it is determined that the monitoring function of the clock frequency fluctuation monitoring unit 69 has an abnormality, and then processing proceeds to Step S14.

On the other hand, when the normality flag Fn2 is set to “0” in Step S18, and the occurrence of an abnormality is recognized, processing then proceeds to Step S19. In Step S19, the monitoring unit diagnosing units 71A and 71B switches to the initial diagnostic normal mode by the clock signal selecting circuits 72A and 72B selecting the regular clock signal CPu (the switch SWa of FIG. 16 is turned on).

Next, in Step S20, the monitoring unit diagnosing units 71A and 71B stand by until the initial diagnostic normal mode becomes stable, and they then determine whether both of the normality flags Fn1 and Fn2 are set to “1” in the same manner as in Step S13 and the occurrence of an abnormality is confirmed. When it is confirmed that the normality flag Fn1 (or Fn2) is reset to “0” and an abnormality has occurred, it is determined that there is an abnormality with the monitoring function of the clock frequency fluctuation monitoring unit 69, and then processing proceeds to Step S14.

On the other hand, when it is determined in Step S20 that both of the normal flags Fn1 and Fn2 are set to “1” and that no abnormality has occurred, processing then proceeds to Step S21.

In Step S21, the monitoring unit diagnosing units 71A and 71B determine whether all of the initial diagnoses have been completed. When all the initial diagnoses are not yet completed, processing then returns to Step S11. When all of the initial diagnoses are completed, the initial diagnostic process is then ended.

In this manner, as there is provided the initial diagnostic function for diagnosing the clock frequency fluctuation monitoring unit 69 itself, it is possible to improve the reliability of the monitoring function of the clock frequency fluctuation monitoring unit 69.

Moreover, the diagnosis in the initial diagnostic abnormality mode is performed after diagnosis in the initial diagnostic normal mode to determine whether the abnormality diagnosis is conducted correctly (whether the output from the AND gate 79U (or 79L) is at a low level), when the abnormal clock signal CPaL (or CPaH) is input. At this time, when the output from the AND gate 79U (or 79L) is a high level instead of a low level, it is determined that the clock frequency fluctuation monitoring unit 69 is not functioning normally.

When inputting the abnormal clock signal CPaL (or CPaH), the output from the AND gate 79U (or 79L) is at a low level and when it is determined that the clock frequency fluctuation monitoring unit 69 is functioning normally, the diagnosis in the initial diagnostic normal mode is conducted again. That is, the regular clock signal CPu is input again from each of the clock frequency selecting circuits 72A and 72B to determine whether the abnormality diagnosis is carried out correctly (i.e., the output from each of the AND gates 79U and 79L is at a high level). At this time, when switching of the signals for initial diagnosis is performed normally and the clock frequency fluctuation monitoring unit 69 is functioning normally, the diagnosis is carried out correctly. However, when the signal for initial diagnosis is not selected correctly, the diagnosis is carried out normally, even if the clock frequency fluctuation monitoring unit 69 is functioning normally. In this case, by conducting the initial diagnosis after the regular clock signal CPu and the abnormal clock signals CPaL and CPaH are input in this order followed by inputting the regular clock signal CPu again, it is made possible to determine whether the initial diagnostic function is operating normally.

As mentioned above, according to the diagnostic method of the clock frequency fluctuation monitoring unit 69, there are provided: a setting voltage V1 higher than the peak value within the normal range of the upper-half wave of the filter output VF to be input; and a setting voltage V2 higher than the peak value at the abnormal time along the lower-half wave of the filter output VF to be input. In addition, there are also provided with the regular clock signal CPu and the abnormal clock signals CPaL and CPaH.

In a case where the period in which it is equal to or higher than the setting voltage V1 does not agree with a predetermined abnormal clock period T1, when the regular clock signal CPu is chosen, and the period in which it is equal to or lower than the setting voltage V2 does not agree with the predetermined abnormal clock period T2, it is determined that the clock frequency fluctuation monitoring unit 69 is normal. Moreover, when the abnormally low frequency clock signal CPaL is chosen, and when the period in which it is equal to or higher than the setting voltage V1 does not agree with the predetermined abnormal clock period T1, it is determined that the clock frequency fluctuation monitoring unit 69 is normal. Moreover, when the abnormally high frequency clock signal CPaH is chosen, and when the period in which it is equal to or lower than the setting voltage V2 does not agree with the abnormal clock period T2, it is determined that the clock frequency monitoring unit 65 is normal.

By use of this diagnostic method, it is made possible to determine whether the clock frequency fluctuation monitoring unit 69 is functioning normally. Moreover, when the clock frequency fluctuation monitoring unit 69 has an abnormality, it is determined appropriately whether it is either an abnormally high frequency exceeding an allowable range on the positive side or an abnormally low frequency exceeding the allowable range on the negative side.

(Modifications to the Embodiment)

Furthermore, in the second embodiment described above, the case of inputting the same normal clock period T1 to the comparator CPU1 and CPU2 has been explained. However, the present invention is not limited thereto. That is, the normal clock period to be input to the comparator CPU1 may be set to T1+α (α denotes a predetermined value for determining a dead zone width), and the normal clock period to be input to the comparator CPU2 may be T1−α to provide a dead zone from −α to +α in the normal clock period. Similarly, regarding the comparator CPL1 and CPL2, the abnormality clock period to be input to the comparator CPL1 may be set to T2 +β (β denotes a predetermined value for determining a dead zone width), and the abnormal clock period to be input to the comparator CPL2 may be T2−β to provide a dead zone from −β to +β in the abnormal clock period.

Moreover, in the aforementioned second embodiment, the case of applying two abnormal clock signals including: the abnormally low frequency clock signal CPaL; and the abnormally high frequency clock signal CPaH for the monitoring unit diagnosing units 71A and 71B has been described. The present invention, however, is not limited to this case. That is, either the abnormally low frequency clock signal CPaL or the abnormally high frequency clock signal CPaH may be omitted to simply determine whether the monitoring unit diagnosing units 71A and 71B are normal.

Moreover, as mentioned above, regarding the magnetization signals supplied to the bridge circuit including the coil pair, the magnetization signal generating units 60A and 60B may generate magnetization signals with different respective frequencies, and then output them to bridge circuits, instead of supplying the magnetization signals with a common frequency from the magnetization signal generating units 60A and 60B. In this case, a low-pass filter for prevention of interference may be inserted between the rectifying and smoothing circuit 52A of the signal processing circuit 57A and the noise rejecting filter 54A, and between the rectifying and smoothing circuit 52B of the signal processing circuit 57B and the noise rejecting filter 54B, so as to suppress the electromagnetic interference in the coil pair.

Moreover, the case where the torque sensor 20 has two sets of coil pairs 22A and 22B configured in the form of a duplex system has been explained in the aforementioned second embodiment. However, the present invention is not limited to this configuration. That is, as illustrated in FIG. 3, the coils 22Aa and 22Ab are wound on the magnetic yoke 81A, forming a set of coil pairs, and accordingly, a torque detecting circuit 30 illustrated in FIG. 18 may be configured as a single system by omitting one of the bridge circuits, and also omitting one of the signal processing circuits 59A and 59B, for example, the signal processing circuit 59B.

(Third Embodiment)

A third embodiment of the present invention will be described below.

The third embodiment differs in the configuration of the torque detecting device 30 from the aforementioned first embodiment.

FIG. 19 is a block diagram of a configuration of the torque detecting device 30. The torque detecting device 30 is provided for each of the first and the second coil pair 22A and 22B, and includes signal processing circuits 59A and 59B for processing output signals from each coil pair. The signal processing circuits 59A and 59B are arranged in the controller 15.

The magnetization signal generating unit 60A is connected to the first coil pair 22A, and supplies magnetization current to the coils 22Aa and 22Ab constituting the first coil pair 22A. Moreover, the magnetization signal generating unit 60B is connected to the first coil pair 22B, and supplies a magnetization current to the coils 22Ba and 22Bb constituting the first coil pair 22B. As such, the magnetization currents are supplied from respective, independent magnetization signal generating units to the first and the second coil pair 22A and 22B.

The magnetization signal generating units 60A and 60B generate alternating currents with predetermined excitation frequencies, respectively. Herein, the magnetization signal generating unit 60A generates an excitation frequency of A Hz (first excitation frequency f1), and the magnetization signal generating unit 60B generates an excitation frequency of B Hz (second excitation frequency f2). Note that the excitation frequencies of the magnetization signals generated by the magnetization signal generating units 60A and 60B may be different from each other, or may be the same.

Moreover, the present embodiment uses a technique of dividing the frequency of the clock signal by counting the clock frequency, and then converting it to the above-mentioned excitation frequency for generating the magnetization signal.

That is, the torque detecting device 30 is provided with CLKs 62A and 62B for outputting clock signals, and counters 63A and 63B for counting the clock frequencies. Herein, a commercially available clock, such as a quartz oscillator, is used as the CLK 62A and 62B. Since such a commercially available clock includes a frequency error of approximately 2%, which is high accuracy, it provides a great stabilization of the sensor system's performance.

Note that these magnetization signal generating units 60A and 60B, the CLKs 62A and 62B, and the counters 63A and 63B are included in oscillating circuits.

One ends of the coils 22Aa and 22Ab constituting the first coil pair 22A are connected to the magnetization signal generating unit 60A via electric resistors 61Aa and 61Ab, respectively. Moreover, the other ends of the coils 22Aa and 22Ab constituting the first coil pair 22A are grounded. Similarly, one ends of the coils 22Ba and 22Bb constituting the second coil pair 22B are connected to the magnetization signal generating unit 60B via electric resistors 61Ba and 61Bb, respectively. Moreover, the other ends of the Coils 22Ba and 22Bb constituting the second coil pair 22B are grounded.

The output signal from the first coil pair 22A is a terminal voltage between the coils 22Aa and 22Ab constituting the first coil pair 22A, and the output signal from the second coil pair 22B is a terminal voltage between the coils 22Ba and 22Bb constituting the second coil pair 22B. These output signals are output to the signal processing circuits 59A and 59B, respectively.

The signal processing circuit 59A includes a differential amplifier 51A, a rectifying and smoothing circuit 52A, a low-pass filter 53A, and a noise rejecting filter 54A. On the other hand, the signal processing circuit 59B includes a differential amplifier 51B, a rectifying and smoothing circuit 52B, a low-pass filter 53B, and a noise rejecting filter 54B. Specifically, the low-pass filters 53A and 53B may be included in the rectifying and smoothing circuits 52A and 52B, respectively.

The differential amplifier 51A amplifies output difference between the outputs from the coils 22Aa and 22Ab constituting the first coil pair 22A, that is, the difference between the terminal voltages (terminal voltage difference) of the coil 22Aa and 22Ab, and outputs the resulting signal. The rectifying and smoothing circuit 52A rectifies, smoothes, and outputs the output from the differential amplifier 51A. The output from the rectifying and smoothing circuit 52A passes through the low-pass filter 53A and the noise rejecting filter 54A to remove noise. The resulting signal is then input to the torque calculation unit 56.

Note that since the signal processing circuit 59B has the same configuration as that of the signal processing circuit 59A, the description thereof will be omitted.

The torque calculation unit 56 conducts a predetermined calculation of the steering torque generated in the steering system based on the output (e.g., an average value) from the noise rejecting filter 54A or the noise rejecting filter 54B. The motor control unit 57 supplies to the electric motor 12 drive current, which will generate the steering auxiliary torque for reducing the steering torque given by a driver based on the calculated result from the torque calculation unit 56.

The torque detecting device 30 has a redundant configuration including: the first torque detecting system having the first coil pair 22A and the signal processing circuit 59A; and the second torque detecting system having the second coil pair 22B and the signal processing circuit 59B. The electric power steering device illustrated in FIG. 1 controls the electric motor 12, so as to conduct the steering auxiliary control usually based on the steering torque detected by the first or the second torque detecting system. On the other hand, when a malfunction occurs in the first or the second torque detecting system, it is switched to a malfunction-free system to continue detecting the steering torque and continue the steering auxiliary control.

Moreover, since an abnormality of the steering torque detecting function will adversely affect the steering auxiliary control seriously, the abnormality in the torque detecting function is regularly monitored while the controller 15 is conducting the steering auxiliary control. Herein, clock monitoring units 65A and 65B are provided to monitor whether the CLKs 62A and 62B for generating a magnetization signal are operating normally.

The clock monitoring units 65A and 65B count, in accordance with clock signals output from the CLKs 62A and 62B, the output pulses (CR oscillation pulses) output from CR oscillators 66A and 66B each using a capacitor (C) and a resistor (R). Then, the clock monitoring units 65A and 65B compare the resulting counted values to initial values stored in CR pulse-width memory units (pulse-width memory units) 67A and 67B, respectively to determine whether the clock frequencies are normal. The above-mentioned initial values are obtained by counting the output pulses including initial fluctuation output from the CR oscillators 66A and 66B, in accordance with the clock signals output from the CLKs 62A and 62B beforehand at the time of manufacturing to be stored in the CR pulse-width memory units 67A and 67B, respectively.

FIG. 20 is a block diagram of a configuration of the clock monitoring unit 65A. Note that since the configuration of the clock monitoring unit 65B is the same as the clock monitoring unit 65A, the description thereof will be omitted.

The clock monitoring unit 65A includes: a counter 65Aa for counting CR oscillation pulses in accordance with a clock; comparators 65Ab and 65Ac for comparing the pulse count counted by the counter 65Aa to pulse count for the CR oscillator 66A stored in the CR pulse-width memory unit 67A; and an OR circuit 65Ad to which the outputs from the comparator 65Ab and 65Ac are input.

With such a configuration, the output signal from the OR circuit 65Ad becomes “0” indicating that the clock frequency is normal, when the pulse count counted by the counter 65Aa is equal to the pulse count for the CR oscillator 66A stored in the CR pulse-width memory unit 67A. On the other hand, when the pulse count counted by the counter 65Aa is not equal to the pulse count for the CR oscillator 66A stored in the CR pulse-width memory unit 67A, the output signal becomes “1” indicating s a clock frequency abnormality.

In order to monitor the accuracy of the clock frequency, a technique of providing a clock for monitoring independently and monitoring correctness of the clock frequency based on the difference therebetween is generally used. However, in the case of using this technique, a sensor system using a high-accuracy clock, such as the CLK 62A, necessitates a high-accuracy clock as a clock for monitoring the accuracy of the clock frequency. This increase the cost.

On the other hand, according to the present embodiment, even a combination with the inexpensive CR oscillator 66A allows monitoring of the clock frequency of the CLK 62A with high accuracy. This configuration will eliminate the necessity of an expensive, independent clock for monitoring, and the cost thereof can be reduced.

Moreover, commercially available, high-accuracy resistors include an error of approximately 1%. However, commercially available, high-accuracy capacitors include an error of approximately 5%. Therefore, in light of fluctuation of the CR oscillators due to those errors included, simple comparison of the output pulse from the CR oscillator to the clock signal cannot provide highly accurate monitoring with the noise of approximately 2% or less.

On the other hand, the present embodiment always counts the output pulses including fluctuation from the CR oscillator in accordance with a clock, and compares them to a pre-counted value (initial value), which is counted beforehand at the time of manufacturing in the same way, to as to monitor the clock frequency. Therefore, monitoring the accuracy will be improved up to a level in consideration of a change in temperature characteristics of the CR. That is, the monitoring accuracy can be improved up to approximately 3%. Note that approximately 6%, which is twice that percentage, may be permissible in actuality.

Moreover, the clock monitoring unit 65A has an initial diagnostic function for diagnosing whether a clock frequency monitoring function is operating normally. The initial diagnosis is conducted immediately after the power is turned on (or ignition switch 18 is turned on), and before the controller 15 starts the steering auxiliary control. Note that a flag etc., which indicates that initial diagnosis is being conducted, is set at the time of the initial diagnosis, so as to prevent the controller 15 from using the torque sensor signal (i.e., prevent the steering auxiliary control).

The clock monitoring unit 65A includes switches SW1 and SW2 as an initial diagnostic unit on the previous stage of the clock input terminal of the counter 65Aa. These switches SW1 and SW2 are included so that either thereof is turned on in response to a signal selection command. The switch SW1 is turned on in the regular clock frequency monitoring mode (regular diagnostic mode), whereas the switch SW2 is turned on in the initial diagnostic mode.

That is, in the regular diagnostic mode, the clock pulses output from the CLKs 62A and 62B are input as clocks used by the counter 65Aa. In the initial diagnostic mode before the torque detecting function of the torque detecting device 30 starts operating (particularly before the oscillating circuit starts operating), the counter pulses output from the counter 63A are input instead of the clock pulses output from the CLKs 62A and 62B as a clock used by the counter 65Aa.

In this manner, an abnormal signal is used to calculate the pulse count of the CR oscillator 66A in the initial diagnostic mode. It is determined that the clock frequency monitoring function is operating normally, by determining that the output signal from the OR circuit 65Ad is “1” when the abnormal signal is input.

Moreover, in the initial diagnostic mode, the normal signal and the abnormal signal may be input as diagnosis signals alternately. The normal signal denotes an ideal clock pulse output from the CLK 62A and CLK 62B. The abnormal signal denotes a counter pulse output from the counter 63A. Furthermore, in the initial diagnostic mode, the normal signal may be input again after the normal and the abnormal signal are input.

In this case, by determining the output signal from the OR circuit 65Ad is “0” when the normal signal is input and that the output signal from the OR circuit 65Ad is “1” when the abnormal signal is input, it is determined that the clock frequency monitoring function is operating normally. In this manner, whether the initial diagnostic function is operating normally is determined. Moreover, whether the diagnosis signal is input normally is also determined.

As mentioned above, it is possible to achieve a more reliable redundant torque sensor system by providing and adding an inexpensive excitation frequency monitoring function.

Note that the case where the torque sensor 20 configured as a duplex torque sensor system including two sets of coil pairs 22A and 22B has been explained in the third embodiment. A single torque sensor system, however, including a single set of coil pairs formed by winding the coils 22Aa and 22Ab around the magnetic yoke 81A may be provided, as illustrated in FIG. 3.

(Fourth Embodiment)

A fourth embodiment of the present invention will be described below.

The fourth embodiment differs in the configuration of the torque detecting device 30 from the first embodiment mentioned above.

FIG. 21 is a block diagram of a configuration of the torque detecting device 30.

The torque detecting device 30 is provided with a signal processing circuit 59 for processing the output signals from the coil pair 22. The signal processing circuit 59 is arranged in the controller 15. Herein, the output signals from the coil pair 22 are terminal voltages of the coils 22 a and 22 b, respectively constituting the coil pair 22.

The signal processing circuit 59 includes a differential amplifier 51, a rectifying and smoothing circuit 52, a low-pass filter 53, a noise rejecting filter 54, an A/D conversion unit (AD converter) 55, a correction value memory unit (memory unit) 58, a torque calculation unit 56, and a motor control unit 57. Note that the low-pass filter 53 may be embedded in the rectifying and smoothing circuit 52. Herein, since the structure except for the A/D conversion unit 55 and the correction value memory unit 58 is the same as the signal processing circuits 59A and 59B in FIG. 11, the descriptions thereof will be omitted, and different parts are focused on and will be discussed.

The A/D conversion unit 55 converts an analog signal output from the noise rejecting filter 54 to a digital signal, and outputs the digital signal to the torque calculation unit 56, to be described later. The correction value memory unit 58 stores an offset correction value and a gradient correction value beforehand.

Herein, the offset correction value and the gradient correction value are an offset and a gradient, respectively, used for making the digital torque waveform obtained by A/D-converting an analog torque signal to a digital value to correspond to a predetermined torque waveform.

That is, when a positive offset is given to the digital torque waveform before correction indicated by a solid line c in FIG. 22 a, the corrected digital torque waveform is indicated by a dashed line c1 in FIG. 22A. Similarly, when a negative offset is given to the digital torque waveform before correction indicated by the solid line c in FIG. 22A, the corrected digital torque waveform is indicated by an alternate long and short dash line c2 in FIG. 22A.

Moreover, a positive gradient is given to the digital torque waveform before correction indicated by a solid line b in FIG. 22B, the corrected digital torque waveform is indicated by a dashed line b1 in FIG. 22B. Similarly, when a negative offset is given to the digital torque waveform before correction indicated by the solid line b in FIG. 22B, the corrected digital torque waveform is indicated by an alternate long and short dash line b2 in FIG. 22B.

Note that FIG. 22A and FIG. 22B illustrate the case where the output voltage at a middle point is 2.5 V in 0-5 V system.

In the present embodiment, in order to keep uniformity of the torque property of the torque detecting device 30, the A/D conversion unit 55 converts an analog torque signal output from the noise rejection filter 54 to a digital torque signal, so that the torque calculation unit 56 adjusts the gain and the offset for the digital torque signal.

A numerical value in parentheses ( ) along the vertical axis in FIG. 22A and FIG. 22B shows a value in 12 bits when converted by the A/D conversion unit 55.

That is, in the production process etc., the A/D converter converts the analog torque signal to the digital value for the digital torque waveform beforehand. Afterwards, an offset and a gradient (gain) for a desired torque waveform are calculated based on this digital torque waveform before correction. An offset correction value and a gradient correction value for correction are then calculated and stored in the correction value memory unit 58.

Then, the torque calculation unit 56 corrects an AD output value, which is an output signal from the A/D conversion unit 55, using the offset correction value and the gradient correction value stored in the correction value memory unit 58. The corrected AD output value is output to the electric motor control unit 57 as a torque detecting signal.

FIG. 23 is a block diagram of a configuration of the torque calculation unit 56.

As illustrated in FIG. 23, the torque calculation unit 56 is provided with a calculation unit (first correction and calculation unit) 56 a. The calculation unit 56 a receives an AD output value (AD value) output from the A/D conversion unit 55 and the gradient correction value (set gain value) and the offset correction value (set offset value) stored in the correction value memory unit 58.

The calculation unit 56 a calculates for correction of the AD value before correction using the set gain value and the set offset value. More specifically, the corrected AD output value will be obtained through calculation of: “the AD value before correction”×“the set gain”+“the set offset”. As such, since there is provided a correction and calculation logic for correcting the gain and the offset of the AD output value based on the set gain value and the set offset value stored beforehand, it is possible to keep the torque property uniformly without carrying out a trimmer adjustment.

Moreover, in order to provide a more reliable system, the correction and calculation logic is configured as a duplex system, and either of them calculates in the same way. Furthermore, there is provided a monitoring function (correction logic monitoring unit) for comparing the calculated results and monitoring abnormality of the correction and calculation logic regularly. When the calculated results from the duplex system are the same (or the difference between the calculated results falls within a predetermined range), it is determined that the correction and calculation logic is normal.

That is, the torque calculation unit 56 is provided with the calculation unit (second correction and calculation unit) 56 b for performing the same computing process as the calculation unit 56 a. The calculation unit 56 b receives an output from a multiplexer (MUX) 56 c as an AD value before correction. The MUX 56 c receives a selection signal (InItCalibSel) to be “1” in a normal state, and the AD output value output from the A/D conversion unit 55 is then input as the AD value before correction.

A comparator 56 d compares the calculated result from the calculation unit 56 a to that from the calculation unit 56 b, and the resulting value is then latched by a latch circuit 56 e. The comparator 56 d outputs “0” when both are the same, whereas it outputs “1” when they are different. The signal latched by the latch circuit 56 e is output as an abnormality detection flag (CalibNGFlg) at a predetermined timing.

When this abnormality detection flag is “0”, the correction and calculation logic is normal. Therefore, the corrected AD output value obtained through the calculation by the calculation unit 56 a is employed and output to the electric motor control unit 57. The torque detecting function continues in this manner. On the other hand, when the abnormality detection flag is “1”, the abnormality processing, such as halting the torque detecting function, is carried out. This allows the prevention of the torque calculation unit 56 from outputting the torque detecting signal with low-reliability.

Furthermore, the torque calculation unit 56 has an initial diagnostic function (initial diagnostic unit) for determining beforehand whether or not the monitoring function of the correction and calculation logic is functioning normally. Different signals are input to the calculation units 56 a and 56 b, respectively to determine that both comparison results differ from each other. This allows the determination that the monitoring function of the correction and calculation logic is functioning normally.

Specifically, a selection signal (InItCalibSel) to be “0” is input to the MUX 56 c at the time of the initial diagnosis, and an inversion signal of the AD output value output from the A/D conversion unit 55 is input to the calculation unit 56 b as an AD value before correction. On the other hand, the AD output value output from the A/D conversion unit 55 is input to the calculation unit 56 a without change.

The comparator 56 d compares the calculated result from the calculation unit 56 a to that from the calculation unit 56 b, so as to determine that an abnormality detection flag (CalibNGFlg) to be “1” is output and to determine that the correction and calculation logic is functioning normally. This initial diagnosis starts, for example, immediately after the power is turned on (or immediately after the ignition switch 18 is turned on) and before the controller 15 starts the steering auxiliary control.

Note that the case where an abnormal signal (inversion signal of the input signal of the calculation unit 57 a) is input to the calculation unit 56 b at the time of the initial diagnosis has been explained. However, the above-mentioned abnormal signal and normal signal (input signals of the calculation unit 57 a) may be input to the calculation unit 56 b alternately. Furthermore, the normal signal may be input again after the normal signal and the abnormal signal are input. In this case, it is determined that the abnormality detection flag (CalibNGFlg) to be “0” is output, when the normal signal is input, and that the abnormality detection flag (CalibNGFlg) to be “1” is output, when an abnormal signal is input, so as to confirm that the correction and calculation logic is operating normally.

Referring back to FIG. 21, the electric motor control unit 57 supplies to the electric motor 12 a drive current Ic for generating a steering auxiliary torque to reduce the steering torque given by a driver, based on the calculated result from the torque calculation unit 56.

Meanwhile, a technique of using a trimmer to make gain and offset adjustment for an analog signal is generally used as the technique for keeping uniform torque property of the coil type torque sensor. However, in this case, the more the number of parts increases due to installation of a trimmer, the more skillful operations for the trimmer adjustment in the production process is necessitated. Moreover, since the temperature characteristics are generally large, they control the temperature characteristics of the signal processing circuit greatly.

On the other hand, as mentioned above, it is possible to make the torque property stable according to the present embodiment, without using the trimmer. Therefore, the reduced number of parts and costs due to elimination of the trimmer are achievable. At the same time, in the improved temperature characteristics of the signal processing circuit is also achievable.

Moreover, since the set gain value and the set offset value are stored beforehand in the memory unit, it is possible to adjust the gain and the offset of the digital torque signal through simple calculation, and appropriate torque property is obtainable.

Furthermore, the calculation logic is configured as a duplex system, and it has a monitoring function for always monitoring an abnormality of the calculation logic through the comparison. This halts the torque detecting function etc., when an abnormality occurs in the calculation logic. Therefore, it is possible to output only a reliable torque detecting signalt. Moreover, since the same signal is input to two calculation logics to determine whether or not the both calculation results are the same, it is possible to confirm appropriately using a comparatively simple technique that the calculation logic is functioning normally.

Moreover, an initial diagnostic function is also provided for determining in advance whether or not the above-mentioned monitoring function is functioning normally. When the calculation logic configured as a duplex system receives different signals, respectively, and the comparison results differ from each other, it is determined that the monitoring function is functioning normally. In this manner, since it is possible to determine appropriately that the monitoring function is functioning normally, a more reliable torque detecting signal is provided.

Furthermore, for initial diagnosis, an inversion signal of the signal input to one calculation logic is input to the other calculation logic. Therefore, an abnormal signal may be generated relatively easily, and initial diagnosis may be carried out with a simple configuration.

Note that while the case where the torque sensor 20 is a one-fold torque sensor system having a coil pair 22 is explained in the fourth embodiment, it may be a torque sensor system configured as a duplex system in which coils 22A and 22B are wound around magnetic yokes 81A and 81B, respectively, into two sets of coil pairs, as illustrated in FIG. 12.

(Fifth Embodiment)

A fifth embodiment of the present invention will be described below.

The fifth embodiment has a configuration that is different in the torque detecting device 30 from the above-described embodiment, and that has an additional function of outputting diagnostic information to the ECU.

FIG. 24 is a block diagram of a configuration of the torque detecting device 30. One ends of the coils 22Aa and 22Ab constituting the coil pair 22A are connected to an oscillation unit 60A via respective electric resistors 61Aa and 61Ab. The other ends of the coils 22Aa and 22Ab are grounded. Output signals from the coil pair 22A, which are terminal voltages of the coils 22Aa and 22Ab, are output to a signal processing circuit 31A.

The signal processing circuit 31A includes a main amplification and full-wave rectification unit 32A, a main smoothing unit 33A, a main outputting unit 34A, a sub amplification and full-wave rectification unit) 35A, a sub smoothing unit 36A, and an sub outputting unit 37A. The torque detecting device 30 further includes a monitoring unit 38A, a diagnosis outputting unit 39A, an initial diagnostic unit 40A, a noise filter 41A, and a connector 42A. This torque detecting device 30 is connected to the controller (ECU) 15 via the connector 42A.

The ECU 15 supplies a supply voltage Vcc to each element in the torque detecting device 30 via the connector 42A and the noise filter 41A. On the other hand, the torque detecting device 30 processes the outputs from the coil pair 22A and outputs to the ECU 15 a main torque signal Tm, a sub torque signal Ts, and a diagnosis signal S, to be described later. The ECU 15 determines whether an abnormality has occurred in the torque detecting device 30, based on the input various signals, and then conducts the steering auxiliary control according to the determination result.

Hereafter, a configuration of the torque detecting device 30 will be explained in detail.

The main amplification and full-wave rectification unit 32A receives the output signals from the coil pair 22A (terminal voltages of the coils 22Aa and 22Ab), and then amplifies and rectifies the difference between these two input voltages. The main smoothing unit 33A smoothes the output wave from the main amplification and full-wave rectification unit 32A. The main outputting unit 34A then outputs the resulting smoothed signal to the ECU 15, as the main torque signal Tm via the noise filter 41A and the connector 42A.

Similarly, the sub amplification and full-wave rectification unit 35A receives the output signals from the coil pair 22A (terminal voltages of the coils 22Aa and 22Ab), and amplifies and rectifies the difference between these two input voltages. The sub smoothing unit 36A smoothes the output waveform from the sub amplification and full-wave rectification unit 35A. The sub outputting unit 37A outputs the smoothed signal to the ECU 15 as the sub torque signal Ts via the noise filter 41A and the connector 42A. Moreover, the output waveform from the sub amplification and full-wave rectification unit 35A is also input to the monitoring unit 38A, to be described later.

The monitoring unit 38A detects a contact failure between the coil 22Aa and the electrical resistor 61Aa and between the coil 22Ab and the electrical resistor 61Ab, for example, by finding a change in differential voltage of a bridged circuit, and detects an abnormality of the circuit system based on the phase difference from a reference voltage (sine wave), not illustrated, which is supplied from the ECU 15. That is, the monitoring unit 38A detects the phase difference between the waveform of an applied alternating current signal and the waveform of the differential voltage from the bridge circuit. When the phase difference exceeds a predetermined value, the monitoring unit 38A determines that a coil, an electric resistor, or a circuit has an abnormality.

Moreover, the diagnosis outputting unit 39A generates a diagnosis signal S indicating diagnostic information of the monitoring unit 38A, and then outputs it to the ECU 15 via the noise filter 41A and the connector 42A. The diagnosis signal S is a fixed cycle of pulse signal as illustrated in FIG. 25A, when the monitoring unit 38A has not detected an abnormality, or in the normal state. On the contrary, it is a fixed low level signal as illustrated in FIG. 25B, while the initial diagnostic unit 40A, to be described later, carries out the initial diagnosis of the monitoring unit 38A. On the other hand, it is a fixed high level signal as illustrated in FIG. 25C, when an abnormality is detected by the monitoring unit 38A.

The initial diagnostic unit 40A starts the operations immediately after the power is turned on (or ignition switch 18 is turned on) and before the ECU 15 starts the steering auxiliary control, and carries out initial diagnosis of whether or not the monitoring unit 38A is operating normally.

Once the initial diagnostic unit 40A starts initial diagnosis, it inputs a normal signal and an abnormal signal alternately to the monitoring unit 38A as initial diagnosis signals, and confirms that the monitoring unit 38A is operating normally; wherein the normal signal denotes a signal that makes the abnormality detection result from the monitoring unit 38A, which is functioning normally, “normal” when abnormality detection is performed using the normal signal. On the other hand, the abnormal signal denotes a signal that makes the abnormality detection result from the monitoring unit 38A, which is functioning normally, “abnormal” when abnormality detection is performed using the abnormal signal.

The ECU 15 determines whether an abnormality occurs in the torque detecting device 30 based on the main torque signal Tm and the sub torque signal Ts.

More specifically, disconnection and or a ground failure is detected by determining whether the main torque signal Tm is equal to or lower than a predetermined value (e.g., 0.3V), and a supply failure is detected by determining whether it is equal to or higher than a predetermined value (e.g., 4.7V). In another manner, disconnection and or a ground failure is detected by determining whether the sub torque signal Ts is equal to or lower than a predetermined value (e.g., 0.3V), and a supply failure is detected by determining whether it is equal to or higher than a predetermined value (e.g., 4.7V). Furthermore, such an abnormality that deviates from crossing characteristics illustrated in FIG. 25 a is detected by determining whether the sum of the main torque signal Tm and the sub torque signal Ts is equal to or higher than a predetermined value (e.g., 5.3 V) or is equal to or lower than a predetermined value (e.g., 4.7 V).

When the diagnosis signal S is a pulse signal illustrated in FIG. 25A, the ECU 15 determines that the torque detecting device 30 is normal based on the main torque signal Tm and the sub torque signal Ts, and it carries out regular, steering auxiliary control using the main torque signal Tm, so as to drive the electric motor 12.

The ECU 15 determines that an abnormality occurs in the torque detecting device 30 based on the main torque signal Tm and the sub torque signal Ts. On the other hand, when the diagnosis signal S is a low level signal illustrated in FIG. 25B, the ECU 15 determines that the initial diagnostic unit 40A is conducting initial diagnosis, and prevents it from carrying out steering auxiliary control.

Moreover, the ECU 15 determines that an abnormality occurs in the torque detecting device 30, based on the main torque signal Tm and the sub torque signal Ts. Yet otherwise, when the diagnosis signal S is a high level signal illustrated in FIG. 25C, the ECU 15 drives the electric motor 12 using a past normal torque value, so as to decrease assist gradually, thereby entering a failsafe mode in which the assist is halted safely.

In this manner, the signal processing circuit 31A in the torque detecting device 30 includes duplex processing circuits (32A to 34A, and 35A to 37A), and outputs two analog signals (main torque signal Tm and sub torque signal Ts).

Moreover, the torque detecting device 30 includes an initial diagnostic unit 40A for monitoring whether the monitoring unit 38A itself is operating normally, and outputs a signal indicating that the initial diagnostic unit 40A is conducting initial diagnosis, as well as the abnormal detection result (normal/abnormal) from the monitoring unit 38A as the diagnosis signal S.

The ECU 15 side detects an abnormality of the torque detecting device 30 based on the diagnosis signal S as well as the two torque signals Tm and Ts output from the torque detecting device 30.

With this configuration, the initial diagnostic unit 40A carries out initial diagnosis of the monitoring unit 38A itself immediately after the power supply is turned on and before the ECU 15 side starts steering auxiliary control. During this initial diagnosis, the diagnosis outputting unit 39A outputs a low level diagnosis signal S illustrated in FIG. 25 b to the ECU 15, and at the same time, the signal processing circuit 31A outputs the main torque signal Tm and the sub torque signal Ts illustrated in FIG. 26B to the ECU 15.

Therefore, the ECU 15 can recognize based on the diagnosis signal S that the monitoring unit 38A is being subjected to initial diagnosis, and prevents use of the main torque signal Tm, thereby preventing steering auxiliary control.

Since the torque detecting device 30 outputs information of during the initial diagnosis as the diagnosis signal S, the ECU 15 can recognize based on the diagnosis signal S that use of the main torque signal Tm is not allowed because the torque sensor system is not yet operating normally.

When the initial diagnosis result from the initial diagnostic unit 40A says that the monitoring unit 38A itself is normal, the torque detecting device 30 will start its torque output function. At this time, when the monitoring unit 38A detects that the torque detecting device 30 is normal, the diagnosis outputting unit 39A outputs a fixed cycle pulse signal illustrated in FIG. 25 to the ECU 15 as the diagnosis signal S. Moreover, as illustrated in FIG. 26A, the signal processing circuit 31A outputs the main torque signal Tm and the sub torque signal Ts to the ECU 15 according to the output signals from the coil pair 22A.

On the other hand, when the monitoring unit 38A detects that an abnormality occurs in the torque detecting device 30, the diagnosis outputting unit 39A outputs a high level diagnosis signal S illustrated in FIG. 25 c to the ECU 15. Moreover, the signal processing circuit 31A outputs the main torque signal Tm and the sub torque signal Ts illustrated in FIG. 26C to the ECU 15.

At this time, since the main torque signal Tm and the sub torque signal Ts deviate from the crossing characteristics illustrated in FIG. 26A, the ECU 15 can determine whether an abnormality occurs in the torque detecting device 30 by monitoring the main torque signal Tm and the sub torque signal Ts. Moreover, since information indicating an abnormality diagnosis result of the monitoring unit 38A is output as the diagnosis signal S, the ECU 15 can determine also based on the diagnosis signal S whether an abnormality occurs in the torque sensor system.

Therefore, since a diagnosis signal S outputting function as well as a function of outputting two kinds of torque signals (i.e., the main torque signal Tm and the sub torque signal Ts) are provided, the torque detecting device 30 will output reliable diagnostic information to the ECU 15. That is, even in the case where neither of the output functions are operating normally, abnormalities can be determined appropriately, thereby entering a failsafe mode. Therefore, the case where it is determined as normal although an abnormality has occurred, and the ECU 15 side thus continues to conduct regular, steering auxiliary control may be prevented, thereby improving reliability.

This is effective in the case where drop in battery voltage occurs instantly during re-ignition of an idling stop vehicle, waiting for a traffic light, etc., and it is thus needed to transmit to the ECU 15 to the effect that the torque signal outputting function will be continued and that performance of the torque signal has deteriorated due to drop in the power supply voltage. Moreover, it is also effective when a problem occurs, such as disagreement in supply voltage between the power supply side and the torque detecting device side.

Moreover, the diagnosis signal S is of three kinds: “abnormality diagnosis results (normal or abnormal)” from the monitoring unit 38A, and “during initial diagnosis”. Each kind is output as a simple, independent signal, so as to configure a simple, reliable communicative function without imposing a heavy load on the ECU 15 side.

Furthermore, the diagnosis signal S is a fixed cycle pulse signal during normality. However, when the diagnosis signal S is disconnected, an abnormality of the diagnosis signal S can be detected by finding the fact that no diagnosis signal S is output. Moreover, when the diagnosis signal S were a low level signal during normality, and when a sensor has a low level fixed failure, it would be undetectable. However, with the aforementioned pulse output, such a failure is also detectable.

As mentioned above, the I/F load on the ECU side may be controlled to a minimum, and sufficient functional safety may be attained.

(Sixth Embodiment)

A sixth embodiment of the present invention will be described below.

This sixth embodiment is provided with a function of setting the sub torque signal Ts to a predetermined fixed value when the monitoring unit 38A in the aforementioned fifth embodiment has detected an abnormality.

FIG. 27 is a block diagram of a configuration of the torque detecting device 30 according to the sixth embodiment. The torque detecting device 30 has the same configuration as the signal processing circuit 31A of FIG. 24 except that it is different from the configuration of the sub outputting unit 37A of the signal processing circuit 31A and the monitoring unit 38A illustrated in FIG. 24. Therefore, parts having a different configuration will be focused on and explained.

The monitoring unit 38A outputs an abnormal signal AB1 to the sub outputting unit 37A when it has detected an abnormality. That is, the monitoring unit 38A detects a difference in phase between the waveform of the applied alternating current signal and the same of the differential voltage of the bridge circuit, and determines that a coil, an electric resistor, or a circuit functions abnormally, and then outputs the abnormal signal AB1 when difference in phase exceeds a predetermined value.

When the sub outputting unit 37A receives the abnormal signal AB1 from the monitoring unit 38A, it will output a sub torque signal Ts of 0V. Moreover, the sub outputting unit 37A outputs the sub torque signal Ts as a fixed value (0V, herein) also during initial diagnosis of the monitoring unit 38A by the initial diagnostic unit 40A.

In this manner, the torque detecting device 30 has the signal processing circuit 31A configured as a duplex processing circuit, which outputs two analog signals (main torque signal Tm and sub torque signal Ts). Once the monitoring unit 38A detects an abnormality, output of the analog signal from the sub side is intercepted (the sub torque signal Ts is set to 0).

With this configuration, the initial diagnostic unit 40A carries out initial diagnosis of the monitoring unit 38A itself immediately after the power supply is turned on and before the ECU 15 side starts steering auxiliary control. During this initial diagnosis, a low level diagnosis signal S illustrated in FIG. 25 b is output to the ECU 15 from the diagnosis outputting unit 39A, and at the same time, the sub torque signal Ts (=0) illustrated in FIG. 28B is output to the ECU 15 from the sub outputting unit 56A.

In this manner, since the torque detecting device 30 outputs information of “during initial diagnosis” as the diagnosis signal S, the ECU 15 can recognize based on the diagnosis signal S that the torque sensor system is not yet operating normally and that use of the main torque signal Tm is not allowed.

Furthermore, during initial diagnosis, since the sub outputting unit 37A starts executing a so-called 0 v outputting sub-function for outputting the sub torque signal Ts (=0), a duplex function of transmitting a signal to the effect that it is during initial diagnosis may be provided, and initial diagnosis (normal functional diagnosis) of the 0 v outputting sub-function can be conducted at the same time. That is, even when the 0 v outputting sub-function is not operating normally, the ECU 15 side can recognize this event. This is the same as the case where an abnormality occurs in the diagnosis signal S.

When it is diagnosed that the monitoring unit 38A itself is normal, based on the initial diagnosis conducted by the initial diagnostic unit 40A, the torque detecting device 30 starts the torque output function. At this time, when the monitoring unit 38A determines that the torque detecting device 30 is normal, the diagnosis outputting unit 39A outputs to the ECU 15 a fixed cycle of pulse signal illustrated in FIG. 25 a as the diagnosis signal S. Moreover, the signal processing circuit 31A outputs the main torque signal Tm and the sub torque signal Ts to the ECU 15 according to the output signals from the coil pair 22A, as illustrated in FIG. 28A.

On the other hand, when the monitoring unit 38A detects that an abnormality occurs in the torque detecting device 30, the diagnosis outputting unit 39A outputs a high level diagnosis signal S illustrated in FIG. 25 c to the ECU 15. Moreover, the signal processing circuit 31A outputs to the ECU 15 the sub torque signal Ts (=0) illustrated in FIG. 28C.

Therefore, the ECU15 can determine whether an abnormality occurs in the torque detecting device 30 by monitoring the main torque signal Tm and the sub torque signal Ts. Moreover, since information of the abnormality diagnosis result of the monitoring unit 38A is output as the diagnosis signal S, the ECU 15 can determine also based on the diagnosis signal S whether an abnormality occurs in the torque sensor system.

As such, the 0 v function for the sub torque signal Ts and the diagnosis signal S outputting function allow provision of a duplex transmitting function of transmitting abnormality information from the torque detecting device 30 to the ECU 15, thereby outputting more reliable diagnostic information. That is, even when the 0 v outputting sub-function is not operating normally, such an abnormality can be determined appropriately based on the diagnosis signal S, thereby entering a failsafe mode. Therefore, the case where it is determined as normal although an abnormality has occurred, and the ECU 15 side thus continues the steering auxiliary control may be prevented, thereby improving reliability.

(Seventh Embodiment)

A seventh embodiment of the present invention will be described below.

The seventh embodiment has two sets of coil pairs in the torque detecting device 30, providing duplex torque detecting systems.

FIG. 29 is a block diagram of a configuration of the torque detecting device 30 according to the seventh embodiment.

The output signals from the coil pair 22A are terminal voltages of the coil 22Aa and 22Ab while output signals from the coil pair 22B are terminal voltages of the coil 22Ba and 22Bb. These output signals are output to the signal processing circuits 31A and 31B, respectively.

The first system of the torque detecting device 30 is provided with the signal processing circuit 31A, the monitoring unit 38A, the diagnosis outputting unit 39A, the initial diagnostic unit 40A, the noise filter 41A, and the connector 42A. The signal processing circuit 31A is provided with the main amplification and full-wave rectification unit 32A, the main smoothing unit 33A, the main outputting unit 34A, the sub amplification and full-wave rectification unit 35A, the sub smoothing unit 36A, and the sub outputting unit 37A.

Moreover, the second system of the torque detecting device 30 is provided with the signal processing circuit 31B, the monitoring unit 38B, the diagnosis outputting unit 39B, the initial diagnostic unit 40B, the noise filter 41B, and the connector 42B as in the first system. The signal processing circuit 31B is provided with the main amplification and full-wave rectification unit 32B, the main smoothing unit 33B, the main outputting unit 34B, the sub amplification and full-wave rectification unit 35B, the sub smoothing unit 36B, and the sub outputting unit 37B.

The torque detecting device 30 is connected to the controller (ECU) 15 via the connectors 42A and 42B.

The ECU1 5 supplies the supply voltage Vcc to each element of the torque detecting device 30 via the connectors 42A and 42B and the noise filters 41A and 41B. On the other hand, the torque detecting device 30 processes the output signals from the coil pairs 22A and 22B, and then outputs to the ECU 15 the main torque signals Tm1 and Tm2 described later and diagnosis signals S1 and S2. The ECU 15 determines based on various input signals whether an abnormality occurs in the torque detecting device 30, and carries out steering auxiliary control in response to the determination result.

A configuration of the torque detecting device 30 will be explained in detail. Since the first and the second system of the torque detecting device 30 have the same configuration, only the first system will be described as an example herein.

The main amplification and full-wave rectification unit 32A receives the output signals from the coil pair 22A (terminal voltages of the coils 22Aa and 22Ab) amplifies, and rectifies difference between these two input voltages. The main smoothing unit 33A smoothes the output waveform of the main amplification and full-wave rectification unit 32A, and the main outputting unit 34A then outputs this to the ECU 15 via the noise filter 41A and the connector 42A as the main torque signal Tm1.

Similarly, the sub amplification and full-wave rectification unit 35A receives the output signals from the coil pair 22A (terminal voltages of the coils 22Aa and 22Ab), and amplifies and rectifies difference between these two input voltages. The sub smoothing unit 36A smoothes the output waveform from the sub amplification and full-wave rectification unit 35A, and the sub outputting unit 37A makes this pass through the noise filter 41A and the connector 42A, resulting in the sub torque signal Ts1. However, the sub outputting unit 37A does not output the sub torque signal Ts1 to the ECU 15. Moreover, the output waveform from the sub amplification and full-wave rectification unit 35A is also input to the monitoring unit 38A described later.

The monitoring unit 38A detects, for example, a contact failure between the coil 22Aa and the electrical resistor 61Aa and between the coil 22Ab and the electrical resistor 61Ab by finding change in differential voltage of the bridge circuit, and detects an abnormality of the circuit system based on phase difference from a reference voltage (sine wave), which is supplied from the ECU 15 but is not illustrated in the drawing. That is, the monitoring unit 38A detects difference in phase between the waveform of the applied alternating current signal and the same of the differential voltage of the bridge circuit, and determines that a coil, an electric resistor, or a circuit functions abnormally, and then outputs an abnormal signal AB1 when difference in phase exceeds a predetermined value.

Moreover, in addition to the signal processing circuit 31A carrying out the abnormality detection processing, the monitoring unit 38A monitors abnormality of the signal processing circuit 31A by comparing the main torque signal Tm1 output from the main smoothing unit 33A to the sub torque signal Ts1 output from the sub smoothing unit 36A. When abnormality occurs, the abnormal signal AB1 is output to the sub outputting unit 37A.

At this time, the sub outputting unit 37A receives the abnormal signal AB1 from the monitoring unit 38A described later, and sets the sub torque signal Ts1 to 0.

The diagnosis outputting unit 39A generates a diagnosis signal S1, which indicates diagnostic information of the monitoring unit 38A, and outputs it to the ECU 15 via the noise filter 41A and the connector 42A.

The initial diagnostic unit 40A starts operation immediately after the power supply is turned on (or ignition switch 18 is turned on) and before the ECU 15 side starts steering auxiliary control, and carries out initial diagnosis of whether the monitoring unit 38A is operating normally.

Once the initial diagnostic unit 40A starts initial diagnosis, it inputs a normal signal and an abnormal signal alternately to the monitoring unit 38A as initial diagnosis signals, and confirms that the monitoring unit 38A is operating normally. At this time, the normal signal may be input again after the normal signal and the abnormal signal are input; wherein the normal signal denotes a signal that makes the abnormality detection result from the monitoring unit 38A, which is functioning normally, “normal” when abnormality detection is performed using the normal signal while the abnormal signal denotes a signal that makes the abnormality detection result from the monitoring unit 38A, which is functioning normally, “abnormal” when abnormality detection is performed using the abnormal signal.

That is, the main torque signal Tm1 and the diagnosis signal S1 are output to the ECU 15 from the signal processing circuit 31A while the main torque signal Tm2 and the diagnosis signal S2 are output to the ECU 15 from the signal processing circuit 31B.

The diagnosis signals S1 and S2 are a fixed cycle pulse signal illustrated in FIG. 30A when the monitoring units 38A and 38B have not detected an abnormality or it is in the normal state; otherwise when the initial diagnostic units 40A and 40B are conducting respective initial diagnoses of the monitoring units 38A and 38B, they are a fixed, low level signal illustrated in FIG. 30B. Furthermore, when the monitoring units 38A and 38B have detected an abnormality or it is in an abnormal state, they are a fixed, high level signal illustrated in FIG. 30C. Moreover, as illustrated in FIG. 31A to FIG. 31C, the main torque signal Tm1 and the main torque signal Tm2 have characteristics in that one increases due to torque as the other decreases accordingly.

The ECU 15 compares the main torque signal Tm1 to the main torque signal Tm2, and determines whether an abnormality occurs in the torque detecting device 30 based on whether it deviates from the normal crossing characteristics.

The ECU15 determines that the torque detecting device 30 is normal, based on the main torque signals Tm1 and Tm2. It carries out regular, steering auxiliary control using the main torque signal Tm1 output from the signal processing circuit 31A, so as to drive the electric motor 12 when the diagnosis signals S1 and S2 are pulse signals as illustrated in FIG. 30A.

On the other hand, when the diagnosis signals S1 and S2 are low level signals as illustrated in FIG. 30B, the ECU15 determines that the initial diagnostic units 40A and 40B are conducting initial diagnosis, and prevents steering auxiliary control from being started.

Moreover, the ECU 15 determines that an abnormality occurs in the torque detecting device 30, based on the main torque signals Tm1 and Tm2. When either diagnosis signal S1 or S2 is a high level signal as illustrated in FIG. 30C, regular, steering auxiliary control is carried out using the main torque signal output from an abnormality-free torque detecting system, thereby driving the electric motor 12.

Note that when both of the diagnosis signals S1 and S2 are a high level signal as illustrated in FIG. 30C, the ECU 15 drives the electric motor 12 using a past normal torque value, so as to decrease assist gradually, thereby entering a failsafe mode in which the assist is halted safely.

Meanwhile, in the case of the torque sensor system having duplex torque detecting systems, the ECU side necessitates duplex signal processing. In particular, when a duplex processing circuit outputs two kinds of signals: the main torque signal and the sub torque signal, the ECU side has to process four kinds of signals altogether, which necessitates double throughput as compared to the single torque detecting system. Moreover, when the signal output is an analog output, the ADC on the ECU side will be needed to accept double throughput. Two ADCs may be needed in light of larger throughput. As such, a larger load will be imposed on the control circuit of the ECU for signal-processing, which adversely influences the throughput, leading to increased cost.

On the other hand, according to the present embodiment, since a single kind of analog signal is output from each of the duplex systems, the ECU 15 will be needed to process only two signals, and the torque detecting system that outputs two kinds of analog signals should thus be the same in throughput as the non-duplex system. Therefore, extension of the ADCs is unnecessary.

Moreover, since a single main torque signal is output from each system, abnormality between the systems may be monitored by comparing the main torque signals Tm1 and Tm2 from respective systems. Thus, an abnormality of sensors is detectable through comparison of two signals without complex signal processing.

Furthermore, when the above-mentioned comparison result points out that an abnormality has occurred, which system has an abnormality may be identified based on the diagnosis signals S1 and S2 output from each system. Therefore, even when either one system or the other has an abnormality, the function of the torque sensor can continue due to the system discrimination, which allows establishment of a more secure, redundant torque sensor system.

Furthermore, since the diagnosis signals S1 and S2 are output from each system as simple signals, a system having an abnormality may be detected using a simple method without imposing a heavy load on the ECU side.

(Modifications to the Embodiment)

Note that the function of outputting diagnostic information according to the above-described fifth to the seventh embodiment is applicable to the torque detecting device 30 according to the first to the fourth embodiment. In this case, the single-fold torque sensor system has the signal processing unit to output the main torque signal and the sub torque signal. On the other hand, the duplex torque sensor system has each signal processing unit to calculate the main torque signal and the sub torque signal, and then outputs only the main torque signal.

APPLICATION

The number of coil pairs may be three or more in each embodiment described above.

Moreover, in each embodiment described above, the case of using the coil-type torque sensor is explained. However, a configuration using a magnetic induction element etc. that outputs two torque signals is also applicable.

INDUSTRIAL APPLICABILITY

According to the abnormality diagnosing method for the torque detecting device of the present invention, initial diagnosis of whether the monitoring circuit itself for monitoring the torque detecting function of the torque detecting device is operating normally may be conducted. This allows provision of a reliable torque detecting device using the abnormality diagnosing method, which is useful.

Moreover, according to the electric power steering device of the present invention, initial diagnosis of the torque detecting device is conducted using the above-mentioned abnormality diagnosing method, so as to determine that the torque detecting device is surely operating normally, and steering auxiliary control may be started afterward. Therefore, stability and reliability of the steering auxiliary control may be improved, which is useful.

REFERENCE SIGNS LIST

-   1 Steering wheel -   2 Steering shaft -   10 Steering auxiliary mechanism -   11 Reduction gear -   12 Electric motor -   15 Controller -   16 Speed sensor -   17 Battery -   18 Ignition switch -   20 Torque sensor -   22A First coil pair -   22Aa, 22Ab, 22Ba, 22Bb Coil -   22B Second coil pair -   30 torque detecting device -   32A, 32B Main amplification and full-wave rectification unit -   33A, 33B Main smoothing unit -   34A, 34B Main outputting unit -   35A, 35B Sub amplification and full-wave rectification unit -   36A, 36B Sub smoothing unit -   37A, 37B Sub outputting unit -   38A, 38B Monitoring unit -   39A, 39B Diagnosis outputting unit -   40A, 40B Initial diagnostic unit -   41A, 41B Noise filter -   42A, 42B Connector -   51A, 51B Differential amplifier -   52A, 52B Rectifying and smoothing circuit -   53A, 53B Low-pass filter -   54A, 54B Noise rejecting filter -   55 A/D conversion unit -   56 Torque calculation unit -   56 a Calculation unit (first correction and calculation unit) -   56 b Calculation unit (second correction and calculation unit) -   56 c MUX -   56 d Comparator -   56 e atch circuit -   57 Motor control unit -   58 Correction value correcting unit -   59A, 59B Signal processing circuit -   60A, 60B Magnetization signal generating unit -   61Aa, 61Ab, 61Ba, 61Bb Electric resistance -   62A, 62B CLK -   63A, 63B Counter -   64A, 64B Abnormality detector -   65A, 65B Clock monitoring unit -   65Aa Counter -   65Ab, 65Ac Comparator -   65Ad OR circuit -   66A, 66B CR oscillator -   67A, 67B CR pulse-width memory unit -   68 Low-pass filter -   69 Clock frequency fluctuation monitoring unit -   69 a Voltage divider -   69 b Window comparator -   69 c Logic circuit -   71A, 71B Monitoring unit diagnosing unit -   72A, 72B Clock signal selecting circuit -   Swa to SWc Switch -   73 a-73 c Frequency divider -   75U, 75L Counter -   76U, 76L OR gate -   77U, 77L Latch circuit -   78U, 78L Determination timing generating circuit -   79U, 79L AND gate -   140 Signal processing circuit -   160 Diagnostic device -   161 Magnetization pulse monitoring unit -   162 Magnetization signal monitoring unit -   162 a Input terminal -   162 b, 162 c Comparator -   162 d, 162 e Counter circuit -   162 f, 162 g Comparator -   162 h OR circuit -   162 i Latch circuit -   162 j Determination timing generating unit -   162 k AND circuit -   163 Phase monitoring unit -   163 a-163 c Comparator -   163 d AND circuit -   163 e Input terminal -   163 f Phase shift circuit -   164 Differential amplitude monitoring unit -   165 MUX/ADC monitoring unit -   165 a MUX -   165 b ADC -   165 c Latch circuit -   165 d Comparator -   165 e OR circuit -   165 f Latch circuit -   165 g Determination timing generating unit -   166 Torque signal monitoring unit -   167 Communication monitoring unit 

The invention claimed is:
 1. An abnormality diagnosing method of a torque detecting device, wherein the torque detecting device comprises at least: a coil pair for detecting a relative displacement between a first rotary shaft and a second rotary shaft, which are connected to each other via a torsion bar that generates a twist when receiving a torque, by corresponding the relative displacement to a change in impedance; a signal processing unit having a torque detecting function for processing an output signal from the coil pair when a magnetization signal is supplied to the coil pair, and outputting a torque detecting signal; and a monitoring unit for regularly monitoring an abnormality of the torque detecting function; the abnormality diagnosing method comprising: inputting a diagnosis signal to the monitoring unit before the torque detecting function starts an operation; and confirming that the monitoring unit is operating normally, and wherein the monitoring unit is a magnetization signal monitoring unit for monitoring a waveform of the magnetization signal, and the monitoring unit receives a normal signal having an ideal waveform of the magnetization signal, and an abnormal signal different in frequency from the normal signal as signals for diagnosis, instead of the magnetization signal to be monitored, for determining whether or not the magnetization signal monitoring unit is operating normally.
 2. The abnormality diagnosing method of the torque detecting device of claim 1, wherein a signal having one half the frequency of the normal signal is input as the abnormal signal, for determining whether or not the magnetization signal monitoring unit is operating normally.
 3. The abnormality diagnosing method of the torque detecting device of claim 1, wherein the monitoring unit is a phase monitoring unit for monitoring whether or not the torque detecting signal shifts a phase from that of the magnetization signal, and the monitoring unit receives the magnetization signal and the signal having the phase shifted from the magnetization signal via a phase shift circuit, as diagnosis signals, instead of the torque detecting signal to be monitored, for determining whether or not the phase monitoring unit is operating normally.
 4. The abnormality diagnosing method of the torque detecting device of claim 1, wherein: the signal processing unit is configured to A/D-convert the torque detecting signal and output the resulting signal, and the monitoring unit is an ADC monitoring unit for monitoring an output value a voltage value to be monitored after an A/D conversion, and the monitoring unit receives a plurality of normal voltage values including a central voltage value within a regularly used voltage region of the torque detecting signal and a plurality of abnormal voltage values different from the normal voltage value, as diagnosis signals, instead of the voltage value to be monitored, for determining whether or not the ADC monitoring unit is operating normally.
 5. The abnormality diagnosing method of the torque detecting device of claim 1, wherein: the signal processing unit comprises a counter for frequency-dividing the clock signal and generating a pulse with an excitation frequency of the magnetization signal, the monitoring unit comprises a CR oscillator and a pulse width memory unit for calculating a width of an output pulse of the CR oscillator using the clock signal, and the monitoring unit is a clock monitoring unit for monitoring an abnormality of the clock signal by calculating the width of the output pulse of the CR oscillator using the clock signal and comparing the calculated value to the width of the output pulse stored in the pulse width memory unit, and the monitoring unit receives the pulse with the excitation frequency generated by the counter, as a diagnosis signal, instead of the clock signal to be monitored, for determining whether or not the clock monitoring unit is operating normally.
 6. The abnormality diagnosing method of the torque detecting device of claim 1, wherein: the signal processing unit comprises an oscillation unit for generating, based on a clock pulse, the magnetization signal with a sinusoidal wave to be supplied to the coil pair, the monitoring unit comprises a low-pass filter for monitoring, the low-pass filter receiving the magnetization signal output from the oscillation unit, and the monitoring unit is a clock frequency change monitoring unit for detecting a change in amplitude of an output from the low-pass filter, as a change in frequency of the clock pulse, and receives a regular clock signal and an abnormal clock signal different in an excitation frequency from the regular clock signal, as diagnosis signals, for determining whether or not the clock frequency change monitoring unit is operating normally.
 7. The abnormality diagnosing method of the torque detecting device of claim 6, wherein: the clock frequency change monitoring unit has a configuration for detecting whether or not at least either a peak value along an upper half wave of the output from the low-pass filter for monitoring or a lower-half wave of the output falls within a normal amplitude range, and receives two kinds of signals including an abnormal high frequency clock signal having a frequency higher than an allowable upper-limit frequency of the regular clock signal, and an abnormal low frequency clock signal having a frequency lower than an allowable lower-limit frequency for the regular clock signal, as the abnormal clock signals, for determining whether or not the clock frequency change monitoring unit is operating normally.
 8. The abnormality diagnosing method of the torque detecting device of claim 1, wherein the signal processing unit further comprises: an AD converter for converting an analog signal corresponding to the torque to a digital signal; a memory unit for storing beforehand a gain correcting value and an offset correcting value for correcting a gain and an offset for the digital signal converted by the AD converter; a first correction and calculation unit for correcting the digital signal converted by the AD converter based on the gain correcting value and the offset correcting value stored in the memory unit and outputting the corrected value as the torque detecting signal; and a second correction and calculation unit for performing the same correcting operation as that of the first correction and calculation unit; and the monitoring unit is an operating logic monitoring unit for inputting the same signal to the first correction and calculation unit and the second correction and calculation unit to compare calculated results of the first correction and calculation unit and the second correction and calculation unit, and monitor whether or not the operating logic of the first correction and calculation unit is functioning normally, and in determining whether or not the operating logic monitoring unit is functioning normally, whether or not the operating logic monitoring unit is operating normally is determined by inputting to the second correction and calculation unit a different signal than that of the first correction and calculation unit, as a diagnosis signal, to confirm that the calculated results of the first correction and calculation unit and the second correction and calculation unit differ.
 9. The abnormality diagnosing method of the torque detecting device of claim 8, wherein an inverted signal of the input signal to the first correction and calculation unit is used as a different signal to be input to the second correction and calculation unit from that to be input to the first correction and calculation unit, for determining whether or not the operating logic monitoring unit is operating normally.
 10. The abnormality diagnosing method of the torque detecting device of claim 1, wherein the signal processing unit is provided to correspond to the coil pair, is configured to output a main torque signal and a sub torque signal based on the output signals from the coil pair, and detects the abnormality of the torque detecting device based on diagnostic information including an abnormality diagnosis result from the monitoring unit, the main torque signal, and the sub torque signal.
 11. The abnormality diagnosing method of the torque detecting device of claim 10, wherein the sub torque signal when an abnormality is detected by the monitoring unit is a predetermined fixed value.
 12. The abnormality diagnosing method of the torque detecting device of claim 10, wherein the diagnostic information includes at least three kinds of information including: information that the abnormality diagnosis result from the monitoring unit is normal, information that the abnormality diagnosis result from the monitoring unit is abnormal, and information that whether or not the monitoring unit is operating normally is being confirmed.
 13. The abnormality diagnosing method of the torque detecting device of claim 12, wherein the diagnostic information is a pulse signal of a fixed period, when the abnormality diagnosis result from the monitoring unit is normal, a high level signal, when the abnormality diagnosis result from the monitoring unit is abnormal, and a low level signal, when whether or not the monitoring unit is operating normally is being confirmed.
 14. The abnormality diagnosing method of the torque detecting device of claim 1, wherein the signal processing unit is provided to correspond to two coil pairs, is configured, to output a main torque signal based on each of the output signals from the coil pairs, and detects an abnormality of the torque detecting device based on diagnostic information including the abnormality diagnosis result from the monitoring unit, and each main torque signal.
 15. The abnormality diagnosing method of the torque detecting device of claim 14, wherein the signal processing unit is configured to calculate the main torque signal and the sub torque signal based on output signals from the coil pairs and output only the main torque signal, and the abnormality diagnosis result from the monitoring unit is a result from the monitoring unit for monitoring the abnormality of the signal processing unit by comparing the main torque signal to the sub torque signal.
 16. An electric power steering device, comprising: a torque detecting device for detecting a steering torque to be input to a steering mechanism; a motor control unit for drive-controlling an electric motor to supply to a steering system a steering auxiliary power that reduces a driver's steering burden, based on at least a steering torque detected by the torque detecting device; and an initial diagnostic unit for diagnosing the torque detecting device using the abnormality diagnosing method of claim 4, before the motor control unit starts drive-controlling the electric motor.
 17. An idling stop vehicle including the electric power steering device of claim
 16. 18. The abnormality diagnosing method of the torque detecting device of claim 1, further comprising: inputting a normal signal and an abnormal signal as signals for diagnosis alternately to the monitoring unit, diagnosing the monitoring unit as normal, when the normal signal is input, and determining the monitoring unit is operating normally when the monitoring unit is diagnosed as abnormal, when the abnormal signal is input.
 19. The abnormality diagnosing method of the torque detecting device of claim 18, wherein the normal signal, the abnormal signal, and the normal signal for diagnosis are input in this order to the monitoring unit. 